Question

A car moving with an initial velocity of 20 m/s steadily increases its velocity to 40 m/s in 20 s. What is its acceleration?

Answer 1

Answer:

Explanation:

Initial velocity of car, u = 20 m/s  

The final velocity will be, v= 0 as the car comes to rest after travelling distance of 40 m (which will be after application of brakes)

 

By third equation of motion we know,  

v2 = u2 + 2 as  

0 = (20)2 + 2 x a x (40)

- 80 a = 400

Thus, a = - 5 m/s2  

Negative sign indicates that it is a retardation.  

When same car is moving with double the velocity  

Initial velocity, u = 2 x 20  =40 m/s  

Thus,  

0 = (40)2 x 2 x (-5) x s  

10 s = 1600

s = 160 m  

Hence, if the same car is travelling at double the velocity the distance travelled by it for same retardation is 160 m