Question

What is the acceleration of a car going 40 mph that slows down to rest over 10 seconds?A. -4 mph/s B. 4 mph/sC. 400 m/s2D. 4 m/s2

Answer 1

`-4(m)/(s^2)`

Step-by-step explanation

the acceleration is the change of velocity in a determined tiem, it can be found by using the expression

`\begin{gathered} g=(\Delta velocity)/(\Delta time)=\frac{v_f-v_i}{\text{time taken}} \\ g=\frac{v_f-v_i}{\text{time taken}} \\ \text{where} \\ v_i\text{ is the initial velocity} \\ v_f\text{ is the final velocity} \\ \end{gathered}`

so

let

`\begin{gathered} v_f=0\text{ (rest)} \\ v_i=40\text{ }(mi)/(h) \\ \text{time}=\text{ 10 sec} \end{gathered}`

replace in the expression

`\begin{gathered} g=\frac{v_f-v_i}{\text{time taken}} \\ g=\frac{0-40(mi)/(h)}{10\text{ s}} \\ g=\frac{-40(mi)/(h)}{10\text{ s}}=-4(mi)/(s^2) \\ g=-4(mi)/(s^2) \end{gathered}`

therefore, the answer is

`-4(mi)/(s^2)`

I hope this helps you