Question

A ball is thrown vertically upward under the influence of gravity. Suppose observer $A$ films this motion and play the tape backwards (so the tape begins with the ball at its highest point and ends with it reaching the point from which it was released), and another observer $B$ observes the motion of the ball from a frame of reference moving at constant velocity which is equal to the initial velocity of the ball. The ball has a downward acceleration according to observer.

• A. $\left(A\right)$ and $\left(B\right)$
• B. only $\left(B\right)$
• C. only $\left(A\right)$
• D. Neither

Answer 1

The correct option is A $\left(A\right)$ and $\left(B\right)$

During ascent ball is going upward therefore its position is positive. Now, though the velocity is decreasing but its direction is upward i.e., positive. Ball is moving under the effect of gravitational acceleration, which is always acting vertically downwards so it is negative. Observer $A$ films this motion and play the tape backwards (so the tape begins with the ball at its highest point and ends with it reaching the point from which it was released), this shows the acceleration is zero $(a_A=0)$ Another observer $B$ observes the motion of the ball from a frame of reference moving at constant velocity which is equal to the initial velocity of the ball, this shows as the frame is moving with constant velocity then the acceleration of the frame
$(a_B=0)$ will be zero which is equal to the initial velocity of ball$(u_b=0)$ going upwards. Acceleration $w.r.t.$ both will be downwards as acceleration of both frames themselves is zero.