Question

An object starts from rest at x=0 m and moves with a constant acceleration of 1.6 m/s^2 along the x-axis during its journey from x=12.8 m to 20.0 m its average velocity will be

Answer 1

Initial velocity = u = 0 m/s

Constant acceleration = a = 1.6 m/s^2

Final velocity and displacement equation is given by  

V² – u² = 2as.

For s = 12.8m, the final velocity is

V² – 0 = 2*1.6*12.8

V = √(40.96) = 6.4 m/s

For s = 20m, the final velocity is  

V² – 0 = 2*1.6*20 = 64  

V = √(64) = 8 m/s

Velocities at 12.8m and 20m are 6.4m/s ad 8m/s.

Since the acceleration is constant, the speed increase at every second is constant.  

That means average of all the numbers is same as average of first and last.  

Hence average velocity = (6.4+8)/2 = 7.2m/s.