Question

A railroad car is moving I the +x direction on a straight and level track. A person in the railroad car throws a ball. The ball follows trajectory shown, relative to the railroad car. From an inspection of the trajectory, what can be concluded about the motion of railroad car? Treat y-axis along vertical.

• A. it is moving at a constant speed
• B. it is speeding up
• C. it is slowing down
• D. none of the above can be concluded

Answer 1

The correct option is C

it is slowing down

= $a^{\prime }\hat{i}-g\hat{j}$

$\therefore a\frac{ball}{car}=a_{ball}-a_{car}$

Only in the x-direction

$\therefore a_{car}=-a^{\prime }$

$\therefore$ For the ball to have such an acceleration w.r.t. the car, the car must have an acceleration of $-a^{\prime }\hat{i}$

hence the car should be slowing down.