Question

If a car at rest accelerates uniformly to a speed of $144km/hr$ in $20s$. Then it covers a distance of

• A. $20m$
• B. $400m$
• C. $1440m$
• D. $2880m$

Answer 1

The correct option is B

$400m$

Step 1: Given data:

At rest a car has speed $u=0$

Final velocity

$$\begin{gathered} v=144kmph \\ v=144\times \frac{5}{18} \\ v=40m/s \end{gathered}$$

The time $t=20sec$

Step 2: Formula used:

Use the 1st equation, we have

$v=u+at$

Now substitute the values

$$\begin{gathered} 40=0+a\times 20 \\ a=2m/s^2 \end{gathered}$$

Now use the motion second law,

$$\begin{gathered} S=ut+\frac{1}{2}a{t}^2 \\ S=0+\frac{1}{2}\times 2{\left(20\right)}^2 \\ S=400m \end{gathered}$$

Therefore the cover distance is $400m$.

Hence, the correct option is (B).