A 7.80-g bullet moving at 680 m/spenetrates a tree trunk to a depth of 5.0cm. (b

Question

A 7.80-g bullet moving at 680 m/spenetrates a tree trunk to a depth of 5.0cm. (b) Assuming the friction force is constant,determine how much time elapses between the moment the bulletenters the tree and the moment it stops moving.
2
A skier of mass 69 kgis pulled up a slope by a motor-driven cable.

(b) What power must a motor have to perform this task?
2 hp
(b) Assuming the friction force is constant,determine how much time elapses between the moment the bulletenters the tree and the moment it stops moving.
2
A skier of mass 69 kgis pulled up a slope by a motor-driven cable.

(b) What power must a motor have to perform this task?
2 hp

Explanation / Answer

mass of the bullet m = 7.8 g = 0.0078 kg velocity v = 680 m / s depth S = 5 cm = 0.05 m final speed of the bullet v = 0 from the relation   v ^ 2 - u ^ 2 = 2aS from this accleration a = [ v ^ 2 - u^ 2 ] / 2S                                  = 4624000 m / s ^ 2 we know time t = ( v - u ) / a                          = 1.47 * 10 ^ -4 s (b). power P = change in K.E / time                     = ( 1/ 2)mv ^ 2 / t                     = 1.085 * 10 ^ 11 W                     = 1.085 * 10 ^ 11 / 746.3 hp                     = 1.4541 * 10 ^ 8 hp

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