Question

What was the initial speed of a car if its speed is 40 m/s after 5 seconds of accelerating at -4 m/s²?A. 50 m/sB. 60 m/sC. 25 m/sD. 20 m/s

Answer 1

Explanation

The uniformly accelerated motion is a motion that is characterized for having a movement in a straight line and a constant acceleration and different of zero, to find the initial speed we can use the formula:

$\begin{gathered} v_f=v_i+at \\ where\text{ v}_fis\text{ the final speed} \\ v_iis\text{ the initial speed} \\ a\text{ is the acceleration} \\ t\text{ is the time} \end{gathered}$

so

Step 1

a)let

$\begin{gathered} v_f=40\text{ }\frac{m}{s} \\ a=-4\frac{m}{s^2} \\ t=5\text{ s} \end{gathered}$

b) now, replace in the formula and solve for vi

$\begin{gathered} v_{f}=v_{i}+at \\ 40\text{ }\frac{m}{s}=v_i+(-4\frac{m}{s^2})(5) \\ 40=v_i-20 \\ add\text{ 20in both sides} \\ 40+20=v_i-20+20 \\ 60\text{ }\frac{m}{s}=v_i \end{gathered}$

therefore, the answer is

B. 60 m/s

I hope this helps you