WBJEE · Physics · Work Power Energy
A train is moving along the tracks at a constant speed \(\mathrm{u}\). A girl on the train throws a ball of mass \(m\) straight ahead along the direction of motion of the train with speed \(v\) with respect to herself. Then
- A Kinetic energy of the ball as measured by the girl on the train is \(\mathrm{mv}^2 / 2\)
- B Work done by the girl in throwing the ball is \(\mathrm{mv}^2 / 2\)
- C Work done by the train is mvu
- D The gain in kinetic energy of the ball as measured by a person standing by the rail track is \(\mathrm{mv}^2 / 2\)
Answer & Solution
Correct Answer
(C) Work done by the train is mvu
Step-by-step Solution
Detailed explanation
Hint : w.r.t. the girl \(E_k=\frac{1}{2} m v^2\) \(\therefore \mathrm{W}=\Delta \mathrm{E}_{\mathrm{k}}=1 / 2 \mathrm{mv}^2\) Work by the train \(=\left\{\frac{1}{2}(v+u)^2-\frac{1}{2} m u^2\right\}-\frac{1}{2} m v^2\)…
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