### Solution

- When t＜0, the distance covered by the particle is zero.

Therefore, the force on the particle is zero.

- When 0＜ t ＜4s, the particle is moving with a constant velocity.

Therefore, the force will be zero.

- When t＞4s, the particle remains at a constant distance.

Therefore, the force of the particle will be zero.

Impulse at t = 0.

Here, u = 0

v = ¾ = 0.75 m/s

M = 4 kg

Impulse= total change in momentum = mv – mu = m (v – u)

= 4 (0 – 0.75) = -3 kg m/s

Impulse at t= 4s

u = 0.75 m/s, v = 0

Impulse = m (v – u) = 4 (0 – 0.75) = -3 kg m/s

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