Question

A 5,000 kg freight car moving at 2 m/s runs into a 10,000 kg freight car at rest. They couple upon collision and move away as one body at _______.
A) 1 m/s.
B) 1/3 m/s.
C) 2 m/s.
D) 2/3 m/s.

Answer 1

Answer:

option D

Explanation:

given,

mass of the freight car (m) = 5,000 Kg

initial speed of car (u)= 2 m/s

mass of the freight car (M)= 10,000 Kg

initial speed (u')= 0 m/s

speed after collision (V)= ?

using conservation of momentum

m u + M u' = (M + m) V

5000 x 2 + 10000 x 0 = (5000 + 10000) V

$V = \dfrac{10000}{15000}$

$V = \dfrac{10}{15}$

$V = \dfrac{2}{3}$

couples move away with the speed of $V = \dfrac{2}{3}$

Hence, the correct answer is option D