Question

A cheetah, weighing $150 \,kg$, chases a deer, weighing $30 \, kg$, in a straight path. The speed of the cheetah is $20 \,m / s$ and that of the deer is $25 m / s$. The approximate speed of the centre of mass of the pair is

• A. 21 m/s
• B. 24 m/s
• C. 26 m/s
• D. zero

Answer 1

Answer: (A)

21 m/s

Answer 2

Velocity of the centre of mass
$v_{C M}=\frac{m_{1} v_{1}+m_{2} v_{2}}{m_{1}+m_{2}}$
$=\frac{(150 \times 20)+(30 \times 25)}{150+30}$
$=\frac{3750}{180}=21\, m / s$