A ball of mass $50 \,g$ is dropped from a height of $20 \,m$. A boy on the ground hits the ball vertically upwards with a bat with an average force of $200 \,N$, so that it attains a vertical height of $45 \,m$. The time for which the ball remains in contact with the bat is ……….. of a second [Take $g=10 \,m / s ^2$ ]

A spherical body of mass $100 \mathrm{~g}$ is dropped from a height of $10 \mathrm{~m}$ from the ground. After hitting the ground, the body rebounds to a height of $5 \mathrm{~m}$. The impulse of force imparted by the ground to the body is given by : (given $\mathrm{g}=9.8 \mathrm{~m} / \mathrm{s}^2$ )

A student attempts to pull himself up by tugging on his hair. He will not succeed

When the speed of a moving body is doubled