Question

A blue train of mass 50 kg moves at 4 m/s toward a green train of 30 kg initially at rest. The trains collide. After the collision the green train moves with a speed of 3 m/s. What is the final momentum of the blue train?

A. 200 kgm/s
B. 20 kgm/s
C. 110 kgm/s
D. 90 kgm/s

Answer 1

According to the law of conservation of momentum, the total momentum of the system before and after the interaction must be equal.

The total initial momentum of the system is:

P_initial = 50 * 4 + 30* 0 = 200kgm/s

The total final momentum of the system

let the velocity of the blue train is=v

P_final = 30* 3 + 50* v = 200

after solving v=2.2m/sec

the momentum of blue train will be= 50* 2.2=110kgm/s

Answer 2

C. 110 kgm/s

Step-by-step explanation:

Law of Conservation of Momentum states that total momentum before the collision must equal total momentum after the collision.

Momentum = p = mv

x = final velocity of the blue train

(50 kg)(4 m/s) + (30 kg)(0 m/s) = (50 kg)(x) + (30 kg)( 3 m/s)

200 kg·m/s + 0 = (50 kg)(x) + 90 kg·m/s

50 kg(x) = 110 kg·m/s

x = (110 kg·m/s)/(50 kg) = 2.2 m/s

p-final (blue train) = (50 kg)(2.2 m/s) = 110 kg·m/s