# What is the kinetic energy of an object with a mass of 3 kg that has been in freefall for 4 s?

The kinetic energy of the object is $K = 2310 N$
You know that the formula of kinetic energy is $K = \frac{1}{2} m {v}^{2}$
At $t = 0$ $v = 0$, so after $4 s$ the speed of the object will be $v = a t = 9.81 \frac{m}{s} ^ 2 \cdot 4 s = 39.24 \frac{m}{s}$
So $K = 2310 N$