Monique has a mass of 46 kg and she is sitting on a swing that hangs 0.50 m above the ground. Pierre pulls the swing back and releases it when the seat is 1.40 m above the ground. How fast is Monique moving when the swing passes through its lowest point?

Question

Monique has a mass of 46 kg and she is sitting on a swing that hangs 0.50 m above the ground. Pierre pulls the swing back and releases it when the seat is 1.40 m above the ground. How fast is Monique moving when the swing passes through its lowest point?
The answer is 4.2m/s, but I don't know how to arrive at the answer.

bobpursley · Answer

The Potential Energy at the start of the swing has to equal the KE at the bottom. mg(1.40-.50)=1/2 m v^2 v=sqrt((2*.90)g)=4.2 m/s