How can you prove that the potential energy of a stretched spring turns into kinetic energy when you release the spring?

Potential energy+Kinetic energy=Total energy

When you release a spring the velocity increases, therefore the kinetic energy increases ke=1/2*mv^2 and the displacement decreases therefore the potential energy decreases pe=1/2*kx^2.

prolly a beacuse the momentuem the car has increases while going down hill

the chart show the masses and velocities of two colliding objects that stick together after a collision.

according to the law of conservation of momentum, the momentum of the object after the collision is  

answer

1,500

kg • m/s.