A bus decreases its speed from 80 kmh^-1 to 60 kmh^-1 in 5 s. Find the acceleration of the bus.

Given,

Initial velocity (u) = 80 kmh^-1

Convert kmh^-1 to ms^-1 : multiply by $\dfrac{5}{18}$

80 x $\dfrac{5}{18}$ = 22.22 ms^-1

The final velocity (v) = 60 kmh^-1

60 x $\dfrac{5}{18}$ = 16.66 ms^-1

Time (t) = 5 sec

According to the first equation of motion,

v = u + at

or

a = $\dfrac{\text {v - u}}{\text{t}}$

Substituting we get,

a = $\dfrac{16.66 - 22.22}{5}$ = -1.112 ms^-2

∴ the acceleration of the bus is -1.112 ms^-2.

The negative sign indicates that the velocity of the bus is decreasing.