Question

A ball has a mass of 4.0 kg and is moving with a velocity of 15.0 km/h. The ball increased its speed to 30.0 Km/h, then the K.E of the ball will ?

Steps please

Answer 1

OK, we need to find initial KE, final KE and the ratio between them (must be > 1) We’d normally have to start by putting velocity into SI units, but as we’re only after a ratio it won’t matter.

Explanation:

`KE_1 = 1/2m.v^2 = 1/2xx4xx15^2`

`KE_1 = 450`J

`KE_2 = 1/2m.v^2 = 1/2xx4xx30^2`

`KE _2 = 1800`J

The KE has thus gone up by a factor of `(KE_2)/(KE_1) = 1800/450` = 4.

So when velocity doubles, KE goes up by the square of that (in the equation there is a `v^2` term) and `2^2 = 4` times.