Question

What is the kinetic energy of an object with a mass of `3 kg` that has been in freefall for `7 s`?

Answer 1

7kJ of energy

Explanation:

The acceleration on the object is g, or 9.8m/s (assuming no air resistance) This number is a constant that applies to all objects close to the Earth.

Use the equation:

`v_f = v_i + at` (The final velocity is the initial velocity plus the acceleration times time)

In this case, the initial velocity is zero (The object is dropped, not thrown downward) So:

`v_f = at`

`v_f = "gt"`

`v_f = 9.8(m/s^2)*7s`

`v_f = 68.6m/s`

Now for kinetic energy = `(1/2mv^2)`

`KE = 1/2 * 3"kg" * (68.6(m/s))^2`

Which is about `7059` or `7000kJ`