A girl of mass 50 kg stands on a railroad car of mass 75 kg moving with velocity 20 m s- 1 . Now, the girl begins to run with a velocity of 10 m s- 1 with respect to the car in the same direction, as that of the car. The velocity of the car at this instant will be

Question

A girl of mass 50 kg stands on a railroad car of mass 75 kg moving with velocity 20 m s- 1 . Now, the girl begins to run with a velocity of 10 m s- 1 with respect to the car in the same direction, as that of the car. The velocity of the car at this instant will be (A) 20ms- 1 (B) 24ms- 1 (C) 16 m s- 1 (D) 18ms- 1

Tardigrade Admin · Accepted Answer

<img class="img-fluid question-image" alt="Solution" src="https://cdn.tardigrade.in/q/nta/p-dqlzfl9qy9ukquuk.jpg" /> According to the law of conservation of linear momentum, Pi=Pf Longrightarrow (50 + 75)20=50(10 + v)+​75v Longrightarrow 125× 20=50(10 + v)+75v Longrightarrow 5× 20=2(10 + v)+3v Longrightarrow 100=20+2v+3v Longrightarrow 5v=80 Longrightarrow v=16 m s- 1

Q. A girl of mass $50 k g$ stands on a railroad car of mass $75 k g$ moving with velocity $20 m s^{- 1}$ . Now, the girl begins to run with a velocity of $10 m s^{- 1}$ with respect to the car in the same direction, as that of the car. The velocity of the car at this instant will be

$20 m s^{- 1}$

$24 m s^{- 1}$

$16 m s^{- 1}$

$18 m s^{- 1}$

According to the law of conservation of linear momentum,
$P_{i} = P_{f}$
$⟹ (50 + 75) 20 = 50 (10 + v) + 75 v$
$⟹ 125 \times 20 = 50 (10 + v) + 75 v$
$⟹ 5 \times 20 = 2 (10 + v) + 3 v$
$⟹ 100 = 20 + 2 v + 3 v$
$⟹ 5 v = 80 ⟹ v = 16 m s^{- 1}$

Q. A girl of mass 50kg stands on a railroad car of mass 75kg moving with velocity 20ms−1 . Now, the girl begins to run with a velocity of 10ms−1 with respect to the car in the same direction, as that of the car. The velocity of the car at this instant will be

20ms−1

24ms−1

16ms−1

18ms−1