Question

How long will it take a force on 10 N to stop a mass of 2.5 kg which is moving at 20 m/s?

Answer 1

We are going to find acceleration
Force = mass × acceleration
10 = 2.5 × a
$$\begin{gathered} \Rightarrow \frac{10}{2.5}=a \\ \Rightarrow \frac{10\times 10}{2.5\times 10}=a \\ \Rightarrow a=4 \end{gathered}$$
Now, putting these values in the equation:
$$\begin{gathered} v=u+at \\ \Rightarrow 20=0+4\times t \\ \Rightarrow 20=4t \\ \Rightarrow \frac{20}{4}=t \\ \Rightarrow t=5s \end{gathered}$$