Question

When brakes were applied to a car, it retarded uniformly at 5 m/s2 and stopped after 15 s. Find the initial velocity of the car.

Answer 1

Given :-

When brakes were applied to a car , it retarded uniformly at 5 m/s² and stopped after 15 seconds .

Required to find :-

• Initial velocity of the car ?

Equation used :-

v = u + at

Solution :-

Given data :-

When brakes were applied to a car , it retarded uniformly at - 5 m/s² and stopped after 15 seconds .

we need to find the initial velocity of the car .

So,

From the given information we can conclude that ;

• Final velocity of the car ( u ) = 0 m/s²

• Retardation ( a ) = - 5 m/s²

• Time ( s ) = 15 seconds

Using the equation of motion ;

i.e. v = u + at

0 = u + ( - 5 )( 15 )

0 = u + ( - 75 )

0 = u + ( - 75 )

0 = u - 75

0 + 75 = u

75 = u

u = 75

Hence,

• Initial velocity of the car ( u ) = 75 m/s

Additional Information :-

The other equations of the motion are ;

s = ut + ½ at²

v² - u² = 2as

These equations of motion are only applicable when the acceleration of the object is constant .

Here,

s = displacement

u = Initial velocity

v = Final velocity

a = acceleration

t = time

However, negative acceleration is termed as " Retardation " .

Acceleration is a vector quantity .

In some cases , the displacement can be taken in the terms of distance .

But, we can't take distance in terms of displacement .

Answer 2

Answer:

Final velocity , v = o m/s

Acceleration = -5m/s2

Time = 15 sec.

Initial velocity of car = u

v=u+at

0=u+-(5(15)

u=75 m/s