Aspring gun shoots out a plastic ball at speed v. the spring is then compressed twice the distance it was on the first shot. a) by what factor is the spring's potential energy increased? explain. b) by what factor is the ball's speed increased? explain.

a) By a factor 4

The spring potential energy is given by

where

U is the potential energy

k is the spring constant

x is the compression of the spring

In this problem, the spring is compressed twice the initial distance, so:

So the new elastic potential energy will be

So, the spring potential energy will quadruple.

b) By a factor 2

When the gun shoots out the ball, the elastic potential energy is then converted into kinetic energy of the ball:

where

m is the mass of the ball

v is its initial speed

Re-arranging the equation we have

We said that the potential energy has increased by a factor 4, so

U' = 4U

So the new speed of the ball will be

So, the speed will double.

the diagram which shows forces as either balanced = same speed or unbalanced = accelerarting