# physics finding kinetic energy

Discussion in 'Homework Help' started by zelda1850, Feb 21, 2010.

1. ### zelda1850 Thread Starter New Member

Jan 3, 2010
18
0
a 20 kilogram block is placed at the top of a 10 meter long inclined plane. the block starts from rest and slides without friction down the length of the incline

determines the kinetic energy of the block just as it reaches the bottom of the incline

mass = 20 kg
distance = 10 m
height = 10 m

the forumla is ke = 1/2 mv square

but i dont have velocity what is the other forumla i can use to solve this problem?

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Find the slope of the inclined plane and then the analyse the weight of the block into its x-y components The x component is should be in parallel with the inclined plane. Use the x component to find the final velocity of the block and thus its kinetic energy.

Jul 7, 2009
1,585
141
Before worrying about what formulas to use, go back and read your textbook to understand the principles involved first. Read about conservation of energy, kinetic energy, and potential energy. You should then be able to make a statement about what principles are involved here. Once those principles are clear in your mind, the solution is pretty obvious and involves only a couple of simple formulas.

Because there's no friction, the mechanical energies are conserved. If you've studied potential energy, consider the change in potential energy of the block and how it might be related to the kinetic energy of the block.

4. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
There appears to be a misprint. The inclined plan cannot be 10 m long (the hypotenuse) and 10 m high (one of the sides). That would make it a vertical wall and not an inclined plane.

5. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Maybe it does not mean the length of the inclined level itself but its base length.

6. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Plausible. The OP needs to clarify the original question.

7. ### Heavydoody Active Member

Jul 31, 2009
140
11
Does the length of the ramp matter in this situation?

8. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Yes, that is a good point. The length does not really matters, it is the height that matters as to calculate the potential energy of the block. Then the kinetic energy at the end of the incline equals the potential energy assuming no friction.

Good point Heavydoody.

9. ### Heavydoody Active Member

Jul 31, 2009
140
11
One of the benefits of frictionless ramps and drag-free objects...unfortunately, they seem to be somewhat rare...well, except in physics textbooks

10. ### zelda1850 Thread Starter New Member

Jan 3, 2010
18
0
oppps i forgot to add that there was a picture with the question showing that the height was 10 meters

11. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Did you understand how to solve it?

12. ### zelda1850 Thread Starter New Member

Jan 3, 2010
18
0
nope is their a formula?

13. ### Heavydoody Active Member

Jul 31, 2009
140
11
In an isolated system with only conservative forces,
ΔK+ΔU=0.
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