4. If a car at rest accelerates uniformly to a speed of 144 km/h in 20 s, it covers a distance of ?

4. If a car at rest accelerates uniformly to a speed of 144 km/h in 20 s, it covers a distance of ?

(a) 2880 m

(b) 1440 m

(c) 400 m

(d) 20 m

Answer :  (c) 400 m

\(144\times\frac{1000\,\text{m}}{3600\,\text{s}} = 40\,\text{m/s}\)

\(144\,\text{km/h} = 40\,\text{m/s}\)

\(a=\frac{v_1-v_2}{t_1-t_2}\)

\(= \frac{40-0}{20-0}\)

\(= 2\,\text{m/s}^2\)

\(s=ut+\frac{1}{2}at^2\)

\(= 0+\frac{1}{2}\times 2 \times (20)^2\)

\(= 400\,\text{m}\)