Question

A boy of mass 45 kg running 6 m/s jumps onto a 30 kg trolley moving in the same direction at 1.5 m/s. Their common velocity will be:

option above:

Answer 1

in this question we are using conservation of momentum theory

MV+mv = (M+m)v'

Where :

M- Mass of the boy = 45kg

m- mass of the trolley = 30kg

V- velocity of the boy = 6m/s

v- velocity of the trolley=1.5m/s

v' - common velocity = x

=(45+30) x=(45x6 +30x1.5)

=(75)x=(270+45)

75x=315

x=315/75

x= 4.2m/s.

Hence, the common velocity = 4.2m/s.

hence the correct answer is option (B)

Answer 2

Answer

B.   4.2 m/s

Given:

M-Mass of the boy = 45kg,

m- mass of the trolley = 30kg,

V- Velocity of the boy = 6m/s,

v- velocity of the trolley = 1.5m/s,

v'- common velocity = x

Formula:

MV+mv = (M+m)v'

Solution:

((45 x 6) + (30 x 1.5)) = (45 + 30) x

270 + 45 = 75x

315 = 75x

315/75 = x

4.2 = x

velocity is mention in m/s

v' = 4.2 m/s

option B) 4.2 m/s