If an explosion occurs in a projectile,which force acts on its centre of mass?

On which factors does the stopping distance of a vehicle depend?

$A$ solid ball is suspended from the ceiling of a motor car through a light string. $A$ transverse pulse travels at the speed $60 \text{ cm/s}$ on the string, when the car is at rest. When the car accelerates on a horizontal road, the speed of the pulse is $66 \text{ cm/s}$. The acceleration of the car is nearly $\left(g=10 \text{ m/s}^2\right)$ (in $\text{ m/s}^2$)

$A$ bird weighs $2 \ kg$ and is inside a closed cage of $1 \ kg$. If it starts flying,then what is the weight of the bird and cage assembly in $kg$?

Two observers are moving at a constant velocity $v$ relative to each other along a straight line. They observe a block of mass $m$ moving over a distance $l$ on a rough surface. Which of the following quantities will be the same for both observers?

$A$ man is standing on a spring platform. The reading of the spring balance is $60\, kg$ wt. If the man jumps off the platform,what happens to the reading of the spring balance?