What is the work done by a coolie walking on a horizontal platform with a load on his head?

$A$ ball is dropped from a height of $10 \, m$. If the energy of the ball reduces by $40 \%$ after striking the ground,how much high can the ball bounce back (in $, m$)? $(g = 10 \, m s^{-2})$

$(i)$ $A$ light and a heavy object have the same momentum. What is the ratio of their kinetic energies? Which one has a larger kinetic energy?
$(ii)$ $A$ ball is dropped from a height of $10\, m$. If the energy of the ball reduces by $40\%$ after striking the ground,how high can the ball bounce back? $(g = 10\, m s^{-2})$

State whether the following statement is true or false:
$A$ force does not work, if it produces no motion.

Two bodies of equal masses move with the uniform velocities $v$ and $3v$ respectively. Find the ratio of their kinetic energies.

Define work. How is work measured? When is work done by a force negative?