Sandra Bullock and George Clooney are playing a game of catch in deep space. Bot

Question

Sandra Bullock and George Clooney are playing a game of catch in deep space. Both are initially at rest. George throws a ball at Sandra and Sandra catches the ball over her head. After she catches the ball, which of the following statements are true?.

I. Sandra begins to rotate

II. Sandra’s center of mass begins to translate

III. The total kinetic energy of Sandra and the ball is the same as it was before Sandra catches the ball

IV. The total momentum of Sandra and the ball is the same as it was before Sandra catches the ball

(a) I and II

(b) I, II, III, and IV

(c) II, III, IV

(d) I and IV

(e) I, II, and IV

The correct answer is E. Please explain how you arrived at your answer.

Explanation / Answer

I) True

when Sandra catches the ball, she exerts some force on the ball.

then according to Newton's third law, the ball also exerts the same force on Sandra.

and this force does acts at center of mass.

so, This produces torque on Sandra. so, Sandra will rotate.

II) True

According to law of conservation of momentum Sandra has to move.

m*u = (m + M)*v (here m is mass of ball and u initial velocity of ball, and M is mass of sandra and v is velocity of Sandra and ball velocity after catching)

==> v = m*u/(m + M)

III) Flase

IT is an example for perfect inelastic collision.

so, kinetic energy is not conserved.

Iv) True

As explained above momentum is conserved.

final momentum of Sandra and ball = initial momentum of ball

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