The masses of the javelin, discus, and shot are 0.80 kg, 2.0 kg, and 7.2 kg, res

Question

The masses of the javelin, discus, and shot are 0.80 kg, 2.0 kg, and 7.2 kg, respectively, and record throws in the corresponding track events are about 98 m, 74 m, and 23 m, respectively. (a) Neglecting air resistance, calculate the minimum initial kinetic energies that would produce these throws. javelin discus shot (b) Neglecting air resistance, estimate the average force exerted on each object during the throw, assuming the force acts over a distance of 2.0 m. javelin discuss shot (c) Do your results suggest that air resistance is an important factor?

Explanation / Answer

Let us assume = 45°, so sin(2) = 1

R = v2 x sin2 / g = v2 / g

v2 = R x g

a) Kinetic energy, E = 0.5 x m v2 = 0.5 x m x R x g

Ejavelin = 0.5 x 0.8 x 98 x 9.8 = 384 J

Ediscus = 0.5 x 2 x 74 x 9.8 = 725.2 J

Eshot = 0.5 x 7.2 x 23 x 9.8 = 811.4 J

b) F = W / x = K / x

Fjavelin = 384 / 2 = 192 N

Fdiscus = 725.2 / 2 = 363 N

Fshot = 811.4 / 2 = 406 N

c) Yes, air resistance must affect each of them very differently because the average force the person could throw with, should be the same.

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