Question

A car starts from rest and at the end of 80 seconds has a speed of 25 km/hr. What is the acceleration?

Answer 1

Velocity for an accelerated motion changes as $v(t) = v_0 + a t$, where $v_0$ is initial velocity, $a$ is acceleration and $t$ is time.

In our case, $v_0 = 0$ (start from rest), hence $v(t) = a t$. From the last formula, $a = \frac{v(t)}{t} = \frac{25 \frac{km}{hr}{}}{80 s} = \frac{25 \frac{km}{hr}}{80/3600 hr} = 1125 \frac{km}{hr^2}$