You can think of the work-kinetic energy theorem as a second theory of motion, p

Question

You can think of the work-kinetic energy theorem as a second theory of motion, parallel to Newton's laws in describing how outside influences affect the motion of an object. In this problem, solve parts (a), (b), and (c) separately from parts (d) and (e) so you can compare the predictions of the two theories. A 15. 3-g bullet is accelerated from rest to a speed of 716 m/s in a rifle barrel of length 68. 3 cm. Find the kinetic energy of the bullet as it bullet as it leaves the barrel. Use the work-kinetic energy theorem to find the net work that is done on the bullet. Use the result to part (b) to find the magnitude of the average net force that acted on the bullet while it was in the barrel. Your response differs significantly from the correct answer. Rework your solution from the beginning and check each step carefully. kN Now model the bullet as a particle under constant acceleration. Find the constant acceleration of the bullet that starts from rest and gains a speed of 716 m/s over a distance of 68. 3 cm. Your response is off by a multiple of ten. km/s2 Modeling the bullet as a particle under a net force, find the net force that acted on it during its acceleration. Your response is within 10% of the correct value. This may be due to roundoff error, or you could have a mistake in your calculation. Carry out all intermediate results to at least four-digit accuracy to minimize roundoff error. kN

Explanation / Answer

c) v2 - u2 = 2as

7162 - 02 = 2 x 0.683 x a

a = 375297.22 m/s2

F = ma = (15.3/1000) x 375297.22 = 5742.05 N = 5.742 kN

d) a = 375297.22 m/s2 = 375.30 km/s2

e) f = 5.74 kN

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