A 7.80-g bullet moving at 570 m/spenetrates a tree trunk to a depth of 6.4 cm. (

Question

A 7.80-g bullet moving at 570 m/spenetrates a tree trunk to a depth of 6.4 cm. (a) Use work and energy considerations to findthe average frictional force that stops the bullet.
1 N

(b) Assuming the friction force is constant, determine how muchtime elapses between the moment the bullet enters the tree and themoment it stops moving.
2 (a) Use work and energy considerations to findthe average frictional force that stops the bullet.
1 N

(b) Assuming the friction force is constant, determine how muchtime elapses between the moment the bullet enters the tree and themoment it stops moving.
2

Explanation / Answer

a) Kinetic energy before hit the tree is: KE0 =(1/2) 7.80*10-3 kg *(540m/s)2 =1137.24J let the friction force is F, the work done by friction forcemust equal to KE0 we have: F.s = KE0 F=KE0/s = 1137.24J / 6.4*10-2 m = 17769.38N b) let acceleration be a, we have: -F=ma a = -F/m = -17769.38N / 7.8*10-3 kg = -2278125m/s2 let the time be t, vf = 0 we have: vf = 0 = v + at = 540m/s - 2278125 m/s2t t = 540m/s / 2278125 m/s2 = 2.37*10-4s let the time be t, vf = 0 we have: vf = 0 = v + at = 540m/s - 2278125 m/s2t t = 540m/s / 2278125 m/s2 = 2.37*10-4s

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