Question

A system consists of two objects that collide in a partially elastic collision. Which two properties of the system are conserved by the collision?

a.) momentum and mass

b.) momentum and kinetic energy

c.) momentum and mechanical energy

d.) mass and kinetic energy

Two friends are standing on opposite ends of a canoe. The canoe is at rest with respect to the lake. Then the friend at the north end of the canoe throws a very massive ball to the friend at the south end of the canoe, who catches it. How does the canoe move, if at all, as a result? a.) The canoe accelerates to the south. b.) The canoe remains motionless.

c.) The canoe accelerates to the north

Answer 1

(1)

Partially inelastic collision may causes deformation in shape of the object and hence after collision some part of energy is used up in deforming the shape of each object .Hence kinetic energy is non conserved.

In this kind of deformation due to inelastic collision there will be no potential energy stored in any object . Hence mechanical energy is not conserved. energy lost in many ways like heat , light , sound etc.

ANS. - only mass and momentum will be conserved.

(2)

At first if the friend at the north end throw a massive ball towards the friend at south end , due law of conservation of momentum ball has a velocity Vb towards south and at the same time the whole system (canoe + two friend) has a velocity Vs towards north.

0 (initial momentum) = M(ball) V(ball) + M(system) V(system) .............................(1)

After some time when friend at south end catches the ball then due to change in momentum of ball it exerted a force on the system again applying law of conservation of momentum

initial momentum before catch = momentum after catch

  M(ball) V(ball) + M(system) V(system) = M (system) V(system) ...................(2)

now from equa (1) & (2) we get

  M (system) V(system) = 0

HENCE AT ALL THE CANOE REMAINS MOTIONLESS