Ep= mgh
Ep = 40 x 9.8 x 10
Ep = 3920J
Ep = 3900J (2sf)
Here we can use the work energy theorem

here we know that

as it come to rest finally



now work done by friction force will be given as


Work done by spring force is given as



so now plug in all data above


so above is the friction coefficient
Honestly i don’t know but I’d just guess if I were you
You are at rest with respect to the car.
You are in motion with respect to the School.
Answer:
They will come back at the same time.
Explanation:
The angular velocity equation of ω
where ω is the frequency of the movement, dependent on the angle. But since swings are simple pendulums and their angles of 8 and 4 degrees are small, they will come back to their starting points at the same time.
I hope this answer helps.