Physics please help me

Question

Newton’s cradle is a contraption where metal balls hang from a frame. When one ball is pulled and released, the collision causes one ball on the opposite end to be released. Which type of force can decrease the total momentum of this system 

A) electrostatic force 

B) strong nuclear force 

C) gravitational force 

D) magnetic force 

Answer 1

I do not see how the strong force could be used to decrease the momentum,

but all the other three forces can.

Newton's cradle relies on Earth's gravity to generate the momentum.

The three forces A, C, D can be used to counteract Earth's gravity.