Question

A 10 kg block is moving at 6 m/s, it is slowed to a speed of 2 m/s in 15 s. How much force is required for this to occur?

Answer 1

Find the acceleration:

$$a=\frac{v_f-v_i}{t}=\frac{2-6}{15}=-0.267\text{ m/s}^2.$$

Thus, according to Newton's second law, the force is

$$F=ma=-2.67\text{ N}.$$

The force is negative because it slows down the block.