Your friend who has a mass of 80 kg runs with a velocity of 2

m/s and jumps onto a 2 kg stationary skateboard so that they

both move together. What is the final velocity of your friend

and the skateboard after she jumps onto it?

Assume all momentum is conserved.

Momentum before = momentum after

m₁ u₁ + m₂ u₂ = m₁ v₁ + m₂ v₂

After she jumps on the skateboard, they have the same velocity, so v₁ = v₂ = v.

m₁ u₁ + m₂ u₂ = (m₁ + m₂) v

The skateboard is originally stationary, so u₂ = 0.

m₁ u₁ = (m₁ + m₂) v

Plugging in values and solving:

(80 kg) (2 m/s) = (80 kg + 2 kg) v

v = 1.95 m/s

Round as needed.