A man of 60 kg is running on the road and suddenly jumps into a stationary trolly car of mass 120 kg. Then, the trolly car starts moving with velocity 2 ms$-$1. The velocity of the running man was ___________ ms$-$1, when he jumps into the car.
Answer (integer)
6
Solution
Total momentum of (man + trolley) system is always conserved
<br/><br/>Initially man was moving with velocity v<sub>1</sub> and trolley was at rest, finally both were moving with velocity 2 ms<sup>$-$1</sup> after man jumps on the trolley.
<br/><br/>So,
<br/><br/>$
\Rightarrow \quad m_{1} v_{1}+0=\left(m_{1}+m_{2}\right) v_{2} $<br/><br/>$
\text { Here, } m_{1}=\text { mass of man }=60 \mathrm{~kg} $<br/><br/>$
m_{2}=\text { mass of trolley }=120 \mathrm{~kg} $<br/><br/>$
v_{1}=\text { speed of } \text { man } $<br/><br/>$
v_{2}=\text { speed of man and trolley }=2 \mathrm{~m} / \mathrm{s} $<br/><br/>$
\Rightarrow 60 \times v_{1}=(60+120) \times 2 $<br/><br/>$
\Rightarrow v_{1}=\frac{(60+120) \times 2}{60}=6 \mathrm{~m} / \mathrm{s}
$
About this question
Subject: Physics · Chapter: Rotational Motion · Topic: Centre of Mass
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