A ball is dropped on the floor from a height of 20 m . It rebounds to a height of 5 m . Ball remains in contact with floor for 1 s . The average acceleration during contact is (acceleration due to gravity $=10 \mathrm{~m} / \mathrm{s}^2$ )

A mass ' M ' is suspended by a rope from a rigid support at point ' P ' as shown in figure. Another rope is tied at end ' Q ' and pulled horizontally with a force ' $F$ '. If the rope makes an angle ' $\theta$ ' with vertical then the tension in the string ' PQ ' is

A machine gun fires a bullet of mass 35 gram with a speed of $600 \mathrm{~m} / \mathrm{s}$. The person holding the gun can extract a maximum force of 147 N on it. The number of bullets that can be fired from the gun per second is

The weight of man in a stationary lift is $w_1$ and when it is moving downwards with uniform acceleration ' a ' is $\mathrm{w}_2$. If the ratio $\mathrm{w}_1: \mathrm{w}_2=4: 3$, then the value of ' a ' is ( $\mathrm{g}=$ acceleration due to gravity)