Question

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A car is moving with the initial velocity
15 m/s. Car stoped after 5s by application
of breaks. Find the retardation
(Decelaration)​

Answer 1

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Let’s review the 4 fundamental kinematic equations of motion for constant acceleration (strongly recommend you commit these to memory – they will serve you well):

s = ut + ½at^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 = 15m/s, v = 0, t = 5s and we want to find a, so we use equation (3)

v = u + at

0 = 15 + 5a

a = -15/5 = -3

The acceleration is -3m/s^2, and the negative sign indicates that it is a retardation.