# physics review

zero
A car travels with a constant velocity. The magnitude of the acceleration of the car is –
Westward
A car travels east and its velocity decreases. The acceleration of the car is in which of the following directions?
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the object is slowing down
If the acceleration vector of an object is directed anti-parallel to the velocity vector, then –
the object is speeding up
If the acceleration vector of an object is directed parallel to the velocity vector, then
the object is turning
If the acceleration of an object is always directed perpendicular to its velocity, then
90-180 degrees
The vector A has components Ax<0, and Ay<0, the angle that this vector makes with the positive x-axis must be in the range
270 to 360
The vector A has components Ax>0 and Ay<0, the angle that this vector makes with the positive x-axis must be in the range
x(negative), y(positive)
A 200lb force is pulling on an object, as shown in Fig3-1. The sign of the x and y components of the force are
Ax = Acos0 Bx = -Bcos60 Ay = Acos90 By = Bcos30
Refer to Fig.3-2. The components of vectors A and B are
20lb up
Three boys pull with a 20-lb force on the same object, as shown in Fig.3-4. The resultant force will be
continuously decreases
For a projectile launched horizontally, the vertical component of a projectile’s velocity
remains a non-zero constant
For a projectile launched horizontally, the horizontal component of a projectile’s velocity
the ball is not acted upon by a force in the horizontal direction
A ball rolls off the edge of a table. The horizontal component of the ball’s velocity remains constant during its entire trajectory because
horizontal
You toss a ball to your friend. When the ball reaches its maximum altitude, its velocity is
is g
Consider a thrown ball which has reached its highest point in flight. The magnitude of the acceleration
the stone
A stone is thrown horizontally from the top of a tower at the same instant that a ball is dropped vertically. Which object is traveling faster when it hits the level ground below?
less than its initial speed
You hit a tennis ball over the net. When the ball reaches its maximum height, its speed is
vo
An arrow is shot, from a bow, at an original speed of vo. When it returns to the same horizontal level its speed will be
(vo)(cos)(omega)
You hit a handball too hard, and it lands horizontally on top of a rood. If its original velocity was vo at an angle omega above the horizontal, then it lands on the roof with a velocity of
in half of the time it is in the air
You toss a ball to your friend. The ball reaches its maximum altitude
g downward
A soccer ball is kicked with a velocity of 25m/s at an angle of 45 above the horizontal. What is the vertical component of its acceleration as it travels along its trajectory (neglect air friction)
is constant
You toss a ball to your friend. When the ball reaches its maximum altitude, its acceleration
both bullets hit the ground at the same time
Bullet G is dropped, from rest, at the same time that another bullet H is fired horizontally from a rifle. If both bullets leave from the same height above the ground, then
be over the bomb
A pilot drops a bomb from a plane flying horizontally at a constant speed. When the bomb hits the ground, the horizontal location of the plane will
increase
A package of supplies is dropped from a plane, and one second later a second package is dropped. Neglecting air resistance, the distance between the falling packages will
increase
A package of supplies is dropped from a plane, and one second later a second package is dropped. Neglecting air resistance, the relative velocity of the 1st package viewed from the second will
less than 45
When air resistance is a factor, maximum range is achieved when the projection angle is
the one with the highest maximum elevation, h
Suppose that several projectiles are fired upward. Which one will be in the air longest? (R is range, h is highest elevation, and t is time of flight.)
four times as much
You are serving the volleyball for the second time in a volleyball game. If your ball leaves your hand with twice the velocity it had on your first serve, its horizontal range R (compared to your first serve) would be
30 and 60
An Olympic athlete throws a javelin at four different angles above the horizontal, each with the same speed: 30,40,60,80. Which two throws cause the javelin to land the same distance away?
45
At what angle should a water-gun be aimed in order for the water to land with the greatest horizontal range?
6 times as far
The acceleration of gravity on the moon is only one-sixth of that on earth, the ball would travel
straight across the river
If you want to cross a river in a motorboat in the least amount of time (least time in water), you should head
in a northwesterly direction
You are trying to cross a river that flows due south with a strong current. You start out in your motorboat on the east bank desiring to reach the west from your starting point. You should head your motorboat
Choice 4 – 17.0m Northward 29.4 Eastward
A displacement vector is 34.0m in length and is directed 60.0 east of north. What are the components of this vector?
24.2 m.
A player throws a football 50.0 m at 61.0° north of west. The westward component of the displacement of the football thrown is given by
18.1 m/s
A boy jumps at a speed of 20.0 m/s at an angle of 25.0° above the horizontal. What is the horizontal component of the boy’s velocity?
48.2°
A butterfly moves with a speed of v = 12.0 m/s. The x-component of its velocity is 8.00 m/s. The angle between the direction of its motion and the x-axis must be
11.3 cm
An electron, initially moving at 2.0 × m/s along the +x-axis, experiences a constant acceleration of m/s2 in the +y direction. How far from its starting point is the electron after 4.0 × seconds?
22.6°
A vector has components = 12.0 m and = 5.00 m. What is the angle that vector makes with the x-axis?
8.13 m/s
A ball thrown horizontally from a point 24 m above the ground strikes the ground after traveling horizontally a distance of 18 m. With what speed was it thrown? (in this problem use g = 10 m/ )
19. m/s
Janice throws a stone horizontally from the roof edge of a 50. meter high dormitory. It hits the ground at a point 60. m from the building. What was the initial velocity?
100. m
A plane flying horizontally at a speed of 50.0 m/s and at an elevation of 160. m drops a package of supplies. Two seconds later it drops a second package. How far apart will the two packages land on the ground?
20 m
A girl throws a rock horizontally, with a velocity of 10 m/s, from a bridge. It falls 20 m to the water below. How far does the rock travel horizontally before striking the water? (use g = 10 m/s2)
10. m/s
A basketball is thrown with a velocity of 20. m/s at an angle of 60.° above the horizontal. What is the horizontal component of its instantaneous velocity at the exact top of its trajectory? (Neglect air friction.)
243 m/s
A fighter plane moving 200 m/s fires a projectile with speed 50 m/s in a forward direction. The projectile makes an angle of 30° with the direction of the plane’s motion. What is the speed of the projectile with respect to a stationary observer on the ground?
465. m
John can hit a golf ball 310. m on Earth. On the moon’s surface, g = , so how far could he hit the same ball if he could only achieve half the initial speed at the same angle as that achieved on Earth?
45. m/s
A motorcycle stunt rider wants to jump a 179. m wide canyon. He arranges a ramp on one side so he will be launched pointed 30.° above the horizontal. What minimum speed will be needed to just reach the other side?
28. m
Johnny throws a shotput at an angle of 45.° and it travels a horizontal distance of 30. meters. If he releases the shotput at the same speed but changes the angle to 55.°, what will be the new range (distance)?
0.95 s
A girl throws a stone straight down from a bridge. The stone leaves her hand with speed of 8.00 m/s at a height of 12 m above the water below. How much time does it take for the stone to hit the water?
157 m/s at an angle 7.31° south of east.
A plane is headed eastward at a speed of 156 m/s. A 20.0 m/s wind is blowing southward at the same time as the plane is flying. The velocity of the plane relative to the ground is
0.50 m/s
A swimmer heading directly across a river 200 m wide reaches the opposite bank in 6 min 40 s. She is swept downstream 300 m. How fast can she swim in still water?
1.2 m/s
A swimmer heading directly across a river 200 m wide reaches the opposite bank in 6 min 40 s. She is swept downstream 480 m. What is the speed of the current?
Newtons first law
Galileo’s Law of Inertia is the same as
move with constant velocity in a straight line.
In the absence of an external force, a moving object will
The net force on the object is zero.
An object is moving with constant velocity in a straight line. Which of the following statements is true?
There are also one or more other forces that act on the object with a sum – .
You try to pull an object by tugging on a rope attached to the object with a force . The object does not move at all. What does this imply?
no forces were responsible for your fall.
You are standing in a moving bus, facing forward, and you suddenly move forward as the bus comes to an immediate stop. What force caused you to move forward?
the vector sum of all the forces.
Suppose several forces are acting upon a mass m. The in = m refers to
4.0 m/ .
A force of 120 N is applied to an object whose mass is 30 kg. The object’s acceleration is
16 N
Starting from rest, a 4.0-kg body reaches a speed of 8.0 m/s in 2.0 s. What is the net force acting on the body?
224 N in a direction 26.6° north of west
The following four forces act on a 4.00 kg object:
40.0 N east
A 2.00-kg object moves with constant velocity 3.00 m/s toward the east. Two forces act on the object. The first is a 40.0 N force toward the west. What is the second force that acts on the object?
3.0 N south.
A 1.0-kg object is moving with a constant velocity 2.0 m/s toward the north. There are two forces acting on the object. One of the forces is 3.0 N north. What is the second force that acts on the object?
5 N
Stacy (S) and David (D) are having a tug-of-war by pulling on opposite ends of a 5.0 kg rope. Stacy pulls with a 15. N force. What is David’s force if the rope accelerates toward Stacy at 2.0 m/ ?
10. m/
If a force accelerates 4.5 kg at 40.m/ , that same force would accelerate 18. kg by how much?
4.2 kN
An antitank weapon fires a 3.0 kg rocket which acquires a speed of 50. m/s after traveling 90. cm down a launching tube. Assuming the rocket was accelerated uniformly, what force acted on it?
8.00 N
A 6.00-kg block is in contact with a 4.00-kg block on a frictionless surface as shown in Fig. 4-11. The 6.00-kg block is being pushed by a 20.0-N force toward the 4.00-kg block. What is the magnitude of the force of the 6.00-kg block on the 4.00-kg block?
1.08 × N
A 1300. N gondola car, at a ski lift, is temporarily suspended at the halfway point, causing the wire to sag by 37.0° below the horizontal, as shown in Fig. 4-12. The tension in the cable is
Mg cos θ.
A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The normal reaction force exerted by the plane on the block is
16.5 kN.
Refer to Fig. 4-13. If the train has an acceleration of 5.50 m/ , then the tension force in the coupling between the middle car and the engine car is
27.5 kN
Refer to Fig. 4-13. The wheels of the engine are pushing back with what force?
96. lb
Florence, who weighs 120. lbs, stands on a bathroom scale in an elevator. What will the scale read when the elevator is accelerating downward at 2.0 m/ ?
13. kN
An elevator weighing 10,000. N is supported by a steel cable. Determine the tension in the cable when the elevator is accelerated upward at 3.0 m/ . (g = 9.8 m/s2)
A 42.0 kg block of ice slides down the plane incline 34.0° in Fig. 4-14. Assuming friction is negligible, what is the acceleration of the block down the incline?
5.48 m/
A 42.0 kg block of ice slides down the plane incline 34.0° in Fig. 4-14. Assuming friction is negligible, what is the acceleration of the block down the incline?
-3.0 N
A horizontal force of 5.0 N accelerates a 4.0 kg mass, from rest, at a rate of 0.50 m/ in the positive direction. What friction force acts on the mass?
03.50
A 60.0-kg mass person wishes to push a 120-kg mass box across a level floor. The coefficient of static friction between the person’s shoes and the floor is 0.700. What is the maximum coefficient of static friction between the box and the floor such that the person can push horizontally on the box and cause it to start moving?
0.161
A child pulls a 3.00-kg sled across level ground at constant velocity with a light rope that makes an angle 30.0° above horizontal. The tension in the rope is 5.00 N. Assuming the acceleration of gravity is 9.81 m/s2, what is the coefficient of friction between the sled and the ground?
1.4 × 102 lb
Florence, who weighs 120 lb, stands on a bathroom scale in an elevator. What will she see the scale read when the elevator is accelerating upward at 2.0 m/s2?
0.47
A wooden block slides directly down an inclined plane, at a constant velocity of 6.0 m/s. How large is the coefficient of kinetic friction, μk, if the plane makes an angle of 25.° with the horizontal?
6.7 N
The coefficients of friction for plastic on wood are μs = 0.50 and μk = 0.40. How much horizontal force would you need to apply to a 3.0-lb plastic calculator to start it moving from rest?
velocity increased.
You are standing in a moving bus, and you suddenly fall backward. You can imply from this that the bus’s
the 4-kg mass accelerates 2.5 times faster than the 10-kg mass.
If you push a 4-kg mass with the same force that you push a 10-kg mass from rest, then
Newton’s third law.
Two cars collide head-on. At every moment during the collision, the magnitude of the force the first car exerts on the second is exactly equal to the magnitude of the force the second car exerts on the first. This is an example of
always be -F.
If you exert a force F on an object, the force which the object exerts on you will
The force of collision on the truck is equal to the force of collision on the car.
A 20-ton truck collides with a 1500-lb car and causes a lot of damage to the car.
Newton’s Third Law.
If you blow up a balloon, and then release it, the balloon will fly away as the air rushes out. This is an illustration of
the Earth being pulled up.
When you sit on a chair, the reaction to your weight is
the toy pulling upward on the Earth with an 8-N force
A child’s toy is suspended from the ceiling by means of a string. The Earth pulls downward on the toy with its weight force of 8 N. If this is the “action force,” what is the “reaction force”?
exactly equal to 1500 N.
Batter up! Your bat hits the ball pitched to you with a 1500-N instantaneous force. The ball hits the bat with an instantaneous force, whose magnitude is
equal to its weight.
An arrow is shot straight up. At the top of its path, the net force acting on it is
The sum of the two readings will be 32 kg.
A 16-kg fish is weighed with two spring scales, each of negligible weight, as shown in Fig. 4-2. What will be the readings on the scales?
with an acceleration less than g.
Two identical masses are attached by a light string that passes over a small pulley, as shown in Fig. 4-3. The table and the pulley are frictionless. The masses are moving
the masses will not move.
See Fig. 4.1. If two identical masses are attached by a light cord passing over a massless, frictionless pulley of an Atwood’s machine, but at different heights, and then released, then
Both cars accelerate at a rate of g sin(30°).
Two toy cars (16 kg and 2 kg) are released simultaneously on an inclined plane that makes an angle of 30° with the horizontal. Which statement best describes their acceleration after being released?
Janice will continue down at constant speed.
Planning to elope with her boyfriend, Janice slides down a rope from her fourth story window. As she slides down the rope, she tightens harder on the rope which of course increases the tension in the rope. When the upward tension in the rope equals Janice’s weight
2/3 F.
Two cardboard boxes full of books are in contact with each other on a table, as shown in Fig. 4-4. Box H has twice the mass of box G. If you push on box G with a horizontal force F, then box H will experience a net force of
W sin θ.
You fall, while skiing, and one ski (of weight W) loosens and slides down an icy slope (assume no friction), which makes an angle θ with the horizontal. The force that pushes it down along the hill is
equal to Mg.
A decoration, of mass M, is suspended by a string from the ceiling inside an elevator. The elevator is traveling UPWARD with a constant speed. The tension in the string is
coefficient of static friction, .
A toolbox, of mass M, is resting on a flat board, as shown in Fig. 4-5. One end of the board is lifted up until the toolbox just starts to slide. The angle θ that the board makes with the horizontal, for this to occur, depends on the
the static coefficient of friction is larger than the kinetic coefficient.
To push a piece of heavy furniture across the carpet usually takes more force to get it moving than it takes to keep is moving. This is because
the total force is zero.
An object is dropped from a helicopter. When it reaches terminal velocity
the brick
A brick and a feather fall to the Earth at their respective terminal velocities. Which object experiences the greater force of air friction?
They have the same non-zero angular displacement.
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger angular displacement?
Child A
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger linear displacement?
They have the same non-zero angular speed.
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger angular speed?
They have different speeds, but the same angular velocity.
Marilyn (M) and her sister Sheila (S) are riding on a merry-go-round, as shown in Fig. 7-3 (bird’s-eye view). Which of the following is true?
Child A
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger tangential speed?
centrifugal
James is twirling a rock around a horizontal circle on the end of a string. Fig. 7-4 is a top view (motion is counterclockwise). If the speed is constant what is the acceleration at point A?
Child A
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger centripetal acceleration?
more than g, and pointing up.
A pilot executes a vertical dive. Just before the plane starts to come up from the bottom of the dive, the force on him is
a centripetal acceleration.
A car, driven around a circle with constant speed, must have
no, because the force and the displacement of the object are perpendicular
Does the centripetal force acting on an object do work on the object?
1.4 V.
Two horizontal curves on a bobsled run are banked at the same angle, but one has twice the radius of the other. The safe speed (no friction needed to stay on the run) for the smaller radius curve is V. Therefore, the safe speed on the larger radius curve is
graph a.
The record playing on the turntable of your stereo is rotating clockwise (as seen from above in Fig. 7-5). After turning it off, your turntable is slowing down, but hasn’t stopped yet. The direction of the acceleration of point P (at the left) is
to take the turn at a faster speed
The banking angle in a turn on the Olympic bobsled track is not constant, but increases upward from the horizontal. Coming around a turn, the bobsled team will intentionally “climb the wall,” then go lower coming out of the turn. Why do they do this?
zero
A race car, traveling at a constant speed of 50 m/s, drives around a circular track of radius 250 m. What angular acceleration does it experience?
must have spherical mass symmetry.
For a spherical planet to act like a “point mass”, so that externally , it
It is never beyond the pull of Earth’s gravity.
A spaceship is traveling to the moon. At what point is it beyond the pull of Earth’s gravity?
12 N
A spherically symmetric planet has four times the Earth’s mass and twice its radius. If a jar of peanut butter weighs 12. N on the surface of the Earth, how much would it weigh on the surface of this planet?
to elliptical orbits where r is the average distance.
Kepler’s discovery that / = K applies
one-sixteenth as much.
A satellite encircles Mars at a distance above its surface equal to 3 times the radius of Mars. The acceleration of gravity at the satellite, as compared to the acceleration of gravity on the surface of Mars, is
7.6 km/s.
The speed for a “low” circular orbit about the Earth is about
the same
If the Earth had four times its present mass, what would be its new period of revolution around the sun, compared to its present orbital period?
A satellite in a large diameter circular orbit will always have a longer period of revolution about the Earth than will a satellite in a smaller circular orbit.
The following statements refer to man-made, artificial satellites in orbit around Earth. Which is an accurate statement?
the satellite mass.
Consider a small satellite moving in a circular orbit (radius r) about a spherical planet (mass M). The period does not depend upon
The speed of T is equal to the speed of A.
Satellite A has twice the mass of satellite T, and rotates in the same orbit. Which of the following is true?
g at the satellite.
Consider an Earth satellite in an elliptical orbit. Its centripetal acceleration is
2.5 ms.
A pulsar (a rotating neutron star) emits pulses at a frequency of 0.40 kHz. The period of its rotation is
graph c.
Your starship, the TOP-QUARK, is in a counter-clockwise “parking orbit” around the planet VULCAN, as shown in Fig. 7-6. In order to achieve escape velocity, the direction your retro-rockets should be facing is
What is the angular speed of a record that rotates at 33-1/3 rpm?
A race car, traveling at a constant speed of 50. m/s, drives around a circular track of radius 250. m. What magnitude acceleration does it experience?
1.8 × m/
What is the centripetal acceleration of a point on the perimeter of a bicycle wheel of diameter 70. cm when the bike is moving 8.0 m/s?
4 m/
A flywheel, of radius 1 m, is spinning with a constant angular velocity of 2 rad/s. What is the centripetal acceleration of a point on the wheel’s rim?
18. s
A space station of diameter 40. meters is turning about its axis at a constant rate. What is the period of revolution of the space station if the outer rim experiences an acceleration of 2.5 m/ ?
9.2 km
A jet plane flying 600. m/s experiences an acceleration of 4.0 g when pulling out of the dive. What is the radius of curvature of the loop in which the plane is flying?
40 m/s
A car traveling 20 m/s rounds an 80 m radius horizontal curve with the tires on the verge of slipping. How fast can this car round a second curve of radius 320 m? (Assume the same coefficient of friction between the car’s tires and each road surface.)
g downward
A roller coaster car is on a track that forms a circular loop in the vertical plane. If the car is to just maintain contact with track at the top of the loop, what is the minimum value for its centripetal acceleration at this point?
/rg
A roller coaster car (mass = M) is on a track that forms a circular loop (radius = r) in the vertical plane. If the car is to just maintain contact with the track at the top of the loop, what is the minimum value for its speed at that point?
1.5 min
A future use of space stations may be to provide hospitals for severely burned persons. It is very painful for a badly burned person on Earth to lie in bed. In a space station, the effect of gravity can be reduced or eliminated. With what period of rotation would a doughnut-shaped hospital of 200. m radius have to rotate, if persons on the outer perimeter are to experience 1/10 the gravity effect of Earth?
1.0 g
A horizontal curve on a bobsled run is banked at a 45° angle. When a bobsled rounds this curve at the curve’s safe speed (no friction needed to stay on the run), what is its centripetal acceleration?
A potter’s wheel decelerates from 50 rev/min to 30 rev/min in 5.0 s, with a constant deceleration. What is the magnitude of the deceleration?
A fan is turned off, and its angular speed decreases from 10.0 rad/s to 6.3 rad/s in 5.0 s. What is the magnitude of the angular acceleration of the fan?
5.30 s
How long does it take for a rotating object to speed up from 15.0 to 33.3 rad/s if it has an angular acceleration of 3.45 rad/ ?
2.18 s
How long does it take a wheel that is rotating at 33.3 rpm to speed up to 78.0 rpm if it has an angular acceleration of 2.15 rad/ ?
0.32 revolutions
The flywheel of a machine is rotating at 126 rad/s. Through what angle will the wheel be displaced from its original position after 6.0 s?
1/4 g.
An astronaut goes out for a “space-walk” at a distance above the Earth equal to the radius of the Earth. Her acceleration will be
Child A
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger tangential speed?
equal to its weight.
An arrow is shot straight up. At the top of its path, the net force acting on it is
the masses will not move.
See Fig. 4.1. If two identical masses are attached by a light cord passing over a massless, frictionless pulley of an Atwood’s machine, but at different heights, and then released, then
equal to its weight.
An arrow is shot straight up. At the top of its path, the net force acting on it is

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