# (a) calculate the minimum initial kinetic energies that would produce the throws.

1. Jan 11, 2009

### alevis

1. The problem statement, all variables and given/known data
The masses of the javelin, discus, and shot are 1.0 kg, 2.0 kg, and 8.0 kg, respectively, and record throws in the

corresponding track events are about 98 m, 75 m, and 25 m, respectively. Neglecting air resistance,
(a) calculate the minimum initial kinetic energies that would produce these throws, and
(b) estimate the average force exerted on each object during the throw, assuming the force acts over a distance

of 2.0 m.
(c) Do your results suggest that air resistance is an important factor?

2. Relevant equations
KE = 1/2mv2
PE = mgh

3. The attempt at a solution
1/2mv2 = mgh.
stuck!

2. Jan 11, 2009

### chrisk

Consider the path of the objects. Each is a parabola, and there are two different launch angles (theta +/- 45 degrees) that can produce the same horizontal distance of travel with the exception of a 45 degree launch angle. A particular launch angle will require the minimum amount of kinetic energy (initial velocity). Determine this particular launch angle, then the velocity required to produce the horizontal distance for each object can be determined. Use the frictionless kinematic equations for a projectile to find the velocities.

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