Question

A car starts moving rectilinearly, first with acceleration w = 5.0 m/s² (the initial velocity is equal to zero), then uniformly, and finally, decelerating at the same rate w, comes to a stop. The total time of motion equals τ = 25 s. The average velocity during that time is equal to (v) = 72 km per hour. How long does the car move uniformly?

Answer 1

As the car starts from rest and finally comes to a stop, and the rate of acceleration and deceleration are equal, the distance, as well as the times are taken, are same in these phase of motion. 

Let Δt be the time for which the car moves uniformly. Then the acceleration/deceleration time is τ-Δt/2 each. So,