Question

a moving train is bought to rest within 20 seconds by applying brakes. find the initial velocity, if the retardation due to brake is 2 m/s²​

Answer 1

Let’s review the 4 basic kinematic equations of motion for constant acceleration (this is a lesson – suggest you commit these to memory):

s = ut + ½ at^2 …. (1)

v^2 = u^2 + 2as …. (2)

v = u + at …. (3)

s = (u + v)t/2 …. (4)

where s is distance, u is initial velocity, v is final velocity, a is acceleration and t is time.

In this case, we know u = 20m/s, v = 0 and t = 5s, and we want to find a, so we apply equation (3)

v = u + at

0 = 20 + 5a, so a = -4m/s^2

The acceleration (“retardation”) is -4m/s^2

Answer By shreyas