question_answer 45)

  A car starts from rest and moves along the X-axis with constant acceleration for 8 s. If it then continues with constant velocity. What distance will the car cover in 12 s, since it started from rest?

Answer:

  Given, the car starts from rest, so its initial velocity u = 0 Acceleration, (a) and time (t) = 8 s From first equation of motion, v = u + at On putting a and t = 8 s in above equation, we get So, final velocity v is Again, from second equation of motion,  On putting t = 8 s and a = 5 ms"2 in above equation, we get So, the distance covered in 8 s is 160 m. Given,                                   total time t = 12 s. After 8 s, the car continues with constant velocity i.e., the car will move with a velocity of . So,     remaining time t'= 12 s - 8 s = 4 s The distance covered in the last 4s (s') = Velocity x Time [ Distance = Velocity x Time] = 40 x 4 = 160 m [We have used the direct formula because after 8 s, car is moving with constant velocity i.e., zero acceleration]. Total distance travelled in 12 s from the start D = s + s' = 160 + 160 = 320m