Question

A 120 kg lineman moving west tackles an 80kg football fullback moving east at 8 m/s. After the collision, the 80kg fullback move east at 2m/s and the 120kg lineman moves east at 3m/s. What was the velocity(speed and direction) of the 120kg lineman before the collision ?

Answer 1

Answer:

Given, Initial velocity of 80 kg football is u₂ = 8 m/s, initial velocity of 120 kg lineman is u₁ = ?

Final velocities are v₁ = 3 m/s and v₂ = 2 m/s.

According to conservation of linear momentum, m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂.

From this, v₁ = (m₁v₁ + m₂v₂ - m₂u₂) / m₁ = [ (120 kg) (3 m/s) + (80 kg) (2 m/s) - (80 kg) (8 m/s) ] / (120 kg)

Therefore, initial velocity of 120 kg is u₁ = (360 + 160 - 640) / 120 m/s = -1 m/s.

Magnitude of u₁ is 1 m/s and the direction is toward west (i.e., opposite to east).