Question

A car starts moving rectilinearly (with initial velocity zero) first with an acceleration of $4m{s}^{-2}$ then uniformly and finally decelerating at the same rate till it stops. Total time of journey is $20$ s and average velocity during the journey is $72km{h}^{-1}$. Then,

• A. Total distance travelled by the car is $400m$.
• B. Maximum speed attained during the journey is $40m{s}^{-1}$
• C. Car accelerates for 10s and decelerates also for $10s$
• D. All of the above

Answer 1

The correct option is D All of the above

Given that the average velocity is $72$ km/h $=20$ m/s.
The total time is given to be $25$ seconds.
Thus, the total distance traveled is $25\times 20=500$ meters
Now, if the maximum velocity is $25$ m/s
Then time taken to attain that speed will be $\frac{v}{a}=\frac{25}{5}=5$ seconds.
Also it will take the same amount of time to return back to rest.