Question

Speed time graph of two cars $A$ and $B$ approaching towards each other is shown in figure. Initial distance between them is $60m$. The two cars will cross each other after time (in seconds):

• A. $3$
• B. $2$
• C. $1.5$
• D. $\sqrt{2}$

Answer 1

The correct option is (A): $3$

The total distance is 60 meters

Let after covering x meter by B in time t they meet

So we can write

$x=ut+\frac{1}{2}a{t}^2$

As initial velocity is 0 so

$x=\frac{1}{2}a{t}^2$ ----------(1)

So, for A we can write

$(60-x)=20t-\frac{1}{2}a{t}^2$ (Initial velocity is 20 m/s)-------------(2)

Adding equations 1 and 2

We get,

$60-x+x=20t$

$Or,t=3sec$

Both cars will cross each other after 3 sec.