Question

A car travelling at 36km/h speeds up to 72km/h in 5s. What is its acceleration? If the same car
stops in 20 seconds, find retardation.

Answer 1

Answer:

Acceleration = 2 m/s2

Retardation = 1/2 m/s2

Explanation:

$eq \: of \: motion \: \\ v = u + at \\ 72 \times \frac{5}{18} = 36 \times \frac{5}{18} + a \times 5 \\ 20 = 10 + 5 \: a \\ a = \frac{10}{5} \\ acc = 2 \: \frac{m}{ {s}^{2} }$

Retardation

$v = u + (- a)t \\ 0 = 36 \times \frac{5}{18} - a \times 20 \\ 10a = 20 \\ retardation = \frac{1}{2} \frac{m}{ {s}^{2} }$