1.A 7.80-g bullet moving at 590 m/spenetrates a tree trunk to a depth of 5.1 cm.

Question

1.A 7.80-g bullet moving at 590 m/spenetrates a tree trunk to a depth of 5.1 cm. (a) Use work and energy considerations to findthe average frictional force that stops the bullet.

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

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

Explanation / Answer

   Given that the mass of bullet is m = 7.8 g =7.8*10-3 kg    Initial speed is u = 590 m/s    The penetration depth  d =5.1 cm = 0.051 m -------------------------------------------------------------------------       Finally the bullet stops thenthe final velocity is V = 0 From the equation of motion the accelaration is a= ( V2 -U2 ) /  2d                                                                                    =( 0 -U2 )/  2d                                                                                         =-------- m/s2        Then the force is F =ma                                      =------- N The time taken from equation of motion is V = U +at                                                                t = ( V - u ) /a                                                                   =( 0 - u ) /a                                                                     =- u /a                                                                   =----------- sec    

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