Question

A man of $50\, kg$ mass is standing in a gravity free space at a height of $10 \,m$ above the floor. He throws a stone of $0.5 \,kg$ mass downwards with a speed $2 \,m/s$. When the stone reaches the floor, the distance of the man above the floor will be

• A. 9.9 m
• B. 10.1 m
• C. 10 m
• D. 20 m

Answer 1

Answer: (B)

10.1 m

Answer 2

Since the man is in gravity free space, force on man + stone system is zero.
Therefore centre of mass of the system remains at rest. Let the man goes $x \,m$ above when the stone reaches the floor, then
$M_{man} \times x = M_ {stone} \times 10$
$x= \frac{ 0.5}{50} \times 10$
$x= 0.1 m$
Therefore final height of man above floor $= 10 + x$
$= 10 + 0.1 = 10.1 \,m$