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# How to solve this question?

Two trolley , A and B are travelling towards each other. Trolley A has a mass number of 1kg and velocity of 4m/s and Trolley B has a mass number of 1.5kg and has velocity of 5m/s. Both the trolley has collision and after trolley A started to move in the direction of trolley B with velocity of 0.75. Find the velocity Trolley B.

### 2 Answers

- JOHNLv 711 months ago
u = velocity of A after collision

v = velocity of B after collision

We take direction of motion of A before collision to be the +ve direction

Conservation of momentum:

1 x u + 1.5 x v = 1 x 4 + 1.5 x (-5) = -3.5

u + 1.5v = -3.5

We want v when u = -0.75

1.5v = -3.5 – u = -3.5 –(-0.75) = -2.75

v = -1.8m/s.

B is moving in the –ve direction with a speed 1.83m/s.

- billrussell42Lv 711 months ago
IF you assume this is a perfectly elastic collision, you can use conservation of momentum.

take direction of A to be +, B to be –

initial momentum is 1•4 – 1.5•5 = 4 – 7.5 = –3.5 kgm/s

let V be unknown velocity of B after collision

final momentum = –0.75•1 + 1.5V = –3.5

–0.75 + 1.5V = –3.5

1.5V = –3.5 + 0.75 = –2.75

V = –1.83 m/s