Question

A speeding car changes its velocity from 108 kmh⁻¹ to 36 kmh⁻¹ in 4 s. Calculate its deceleration in

1. ms⁻²
2. kmh⁻².

Answer 1

Initial velocity = u = 108 kmh⁻¹

u = `108xx5/18` m⁻¹

u = 30 ms⁻¹

Final velocity = v = 36 kmh⁻¹

v = `36xx5/18` ms⁻¹

v = 10 ms⁻¹

Time = t = 4 S

Deceleration = a = `("v"-"u")/"t"`

a = `(10-30)/4`

a = `-20/4` = −5 ms⁻²

a = `(-5xx3600xx3600)/1000` kmh⁻² = −64800 kmh⁻²