Exercise (Assertion & Reason)

Assertion : Kinetic energy of a body becomes four times, when its linear momentum is doubled.
Reason : This is because, K.E. = p² /2m.

Assertion: Kinetic energy is conserved in both, perfectly elastic and inelastic collisions.

Reason: Because both types of collisions are identical.

Assertion: In the case of bullets fired from a gun, the ratio of the kinetic energy of gun and bullet is equal to the ratio of the mass of bullet and gun.
Reason: In firing, momentum is conserved.

Assertion: In an elastic collision of two billiards balls, the kinetic energy is not conserved during the short interval of time of collision between the balls.

Reason: Energy spent against friction does not follow the law of conservation of mechanical energy.

Assertion: A rocket launched vertically upward explodes at the highest point it reaches. The explosion produces three fragments with non-zero initial velocity. Then the initial velocity vectors of all the three fragments are in one plane.
Reason: For the sum of the momentum of three particles to be zero, all the three momentum vectors must be coplanar.

Assertion: Quick collisions are more violent than slow collisions.

Reason: Quick collisions are inelastic in nature.

Assertion: If a person jumps from a height with his legs rigid, then his ankle is more injured.

Reason: The force will be maximum on its ankle during the collision with the ground.