Question

A hockey puck sliding on a frictionless surface strikes a box at rest. After the collision, the two objects stick together and move at some final speed. Which of the following describes the change in momentum and energy of the puck during the collision? 

 The puck loses some, but not all, of its original momentum and mechanical energy. 

 One cannot determine if the momentum or energy of the puck is conserved without knowing the final velocities and masses two objects. 

 The puck conserves its original momentum, but loses some, but not all, of its mechanical energy. 

 The puck loses some momentum in the collision, but conserves its mechanical energy. 

 The puck conserves its original momentum and mechanical energy. 

 The puck conserves its original momentum, but loses all of is mechanical energy. 

 Which of the following describe the change in momentum and energy of the combined puck and box during the collision? 

 One cannot determine if momentum or energy of the system is conserved without knowing final velocities masses of the two objects. 

 The system conserves its original momentum, but loses all of its mechanical energy. 

 The system conserves its original momentum and mechanical energy. 

 The system locos some, but not all, of its momentum and mechanical energy. 

 The system loses some momentum in the collision, but conserves its mechanical energy. 

 The system conserves its original momentum, but loses some, but not all, of its mechanical energy.

Answer 1

1)

m = mass of the puck

M = mass of the box

v = initial velocity of puck before collision

V = final velocity of the puck-box combination after collision

using conservation of momentum

mv = (m + M) V

V = mv/(m+ M)

clearly, V < v

multiplying both side by "m"

mV < mv

final momentum of puck after collision < initial momentum of puck before collision

hence the puck lose sum of its momentum.

Since the speed of puck after collision is smaller, hence the mechanical energy after collision is smaller as compared to mechanical energy before collision. hence puck lose some of its mechanical energy too

hence correct choice is A)

2)

in inelastic collision,

final total momentum = initial total momentum

hence change in momentum = final total momentum - initial total momentum

change in momentum = 0

hence the momentum of the system remains conserved.

in inelastic collision , there is loss of energy . hence system lose some of its mechanical energy

hence the correct choice is