An object of mass 2kg moving with a speed 'u'collided with a stationary box , after collision , the object continue in its original direction with one quarter of its initial speed.

If the total kinetic energy of the colliding system remains constant , calculate the mass of the box .

1 answer

Let the mass of the box be 'm'.

Before the collision, the kinetic energy of the system is:

K1 = 1/2 * 2kg * u^2 = u^2

After the collision, the object has one quarter of its initial speed, so its final speed is u/4. The box must have gained momentum in the opposite direction to conserve momentum.

Using conservation of momentum:

Initial momentum = Final momentum

2kg * u = 2kg * (u/4) + m * (u/4)

Simplifying:

u = (m/2 + 1) * (u/4)

4 = m/2 + 1

m/2 = 3

m = 6kg

Therefore, the mass of the box is 6kg.