- A force of 30 N produces an acceleration of 2 m/s2 in a body of mass m. Find the mass of the body. Also, find the acceleration, if force is doubled in magnitude along the same direction.
- A bullet of mass 10 g strikes a sand bag with the speed of 103 m/s after covering the distance of 5 cm.

Based on above information, calculate the following:
- The resistive force exerted by sand on the bullet.
- The time taken by bullet to come to rest.

- Given, F = 30 N, a = 2 m/s
^{2}

So, mass of body, m = = 15 kg [∵ F = ma]

If f is double, a is double as F ∝ a [since, m is constant]

So, a = 4m/s^{2}
- Given, m = 10 g = 0.01 kg,

u = 10^{3}m/s, v = 0

s = 5 cm = 0.05 m
- Acceleration of bullet, a = [From third equation of motion]

Force applied by the bullet, F = 0.01 x -10^{7} = - 10^{5}N [Negative sign shows direction of force against the direction of motion]

The resistive force exerted by the sand on the bullet = 10^{5}
- Time taken by bullet to come to rest, t = = = 10
^{–4} [From first equation of motion]