Question

If a car at rest accelerates uniformly to a speed of 144 $\frac{km}{h}$in 20 sec. It covers a distance of

• A. 20 cm
• B. 400 cm
• C. 1440 cm
• D. 2980 cm

Answer 1

The correct option is B

400 cm

Step 1: Given that

Initial velocity (u) =0.

Final velocity (v) =144 $\frac{km}{h}$ or $144\times \frac{5}{18}=40\frac{m}{s}.$

Time (t) =20 sec.

Step 2: Formula :

v=u+at .

$S=ut+\frac{1}{2}\times a\times t^2.$

Step 3: Calculation :

v=u+at

$$\begin{gathered} 40=a\times 20 \\ a=2\frac{m}{s^2}. \end{gathered}$$

$S=ut+\frac{1}{2}\times a\times t^2.$

$$\begin{gathered} S=0\times 20+\frac{1}{2}\times 2\times {20}^2. \\ S=0+\frac{1}{2}\times 2\times {20}^2. \\ S=400m. \end{gathered}$$

Step 4.

Hence, the distance covered (S) =400 m and option B is the correct answer .