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.

Explanation:

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.

diagram is missing, but i will try to explain your doubt.

answer:

amplitude is the maximum displacement or distance moved on a point of a vibrating body or wave measured from its equilibrium position.it is equal to half the length of vibration path.