Question

If velocity is cut in half, how is the kinetic energy affected

Answer 1

Using the Kinetic Energy formula:
K.E = 1/2 (mv^2)

It is shown that kinetic energy is directly proportional to the square of velocity. Which means that if the velocity was reduced to half, kinetic energy would be 1/4 of the original value. To state an example:

let: m = 1 ; v = 2

Substituting the values would give us:
K.E = 1/2 ((1)(2)^2)
K.E = 2

Halving the value of velocity would give us the following:
K.E = 1/2 ((1)(1)^2)
K.E = 0.5

As seen, K.E was reduced to 1/4 of the original value.

Answer 2

since the K.E proportional to the square of the velocity
so if the velocity cut in half the K.E will equal 1/4 the initial value