Question

a boy with mass 50kg running at 5m/s jumps on to a 20kg trolley travelling in the same direction at 1.5m/s what is their common velocity?<br />

Answer 1

Boy information

Mass = 50kg

Velocity = 5m/s

Trolley information

Mass = 20 kg

Velocity = 1.5 m/s

so using conservation law of momentum

MV + mv = ( M + m ) v'

50*5 + 20*1.5 = ( 50 + 20 ) v'

250 + 30 = 70 v'

280 = 70 v'

so v' = 4m/s which is their common velocity.


Hope it helps!

Answer 2

m1= 50kg
v1 = 5m/s

m2 = 20kg
v2 = 1.5m/s

after jump,
total mass(M)= 50+20 = 70kg
final velocity= v

according to conservation of momentum
Mv = m1v1 + m2v2

70×v = 50×5 + 20×1.5

70v = 280

v = 280/70

v = 4m/s

Their common velocity will be 4 m/s