Question

The speed of car is reduced from 54km/h to 36km/h in a certain time during which it travelled 125m Calculate retardation

Answer 1

Hello Friend....
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In the given question it is clear that the speed of car reduced with respect to time. So, It's a case of accelerated motion.

So, we have to use equation of motion.

Given,

Initial velocity (when observation started) u = 54 km/hr.
u = 54 × 5/18 m/sec (converting km/h into m/sec)
= 15 m/sec

final velocity (when observation ends) v = 36 km/h
v = 36 × 5/18 m/s (converting km/h into m/s)
= 10 m/sec

distance travelled (s) = 125 m

First of all we have to find the acceleration.

by using the formula

v^2 - u^2 = 2as
(10 × 10) - (15 × 15) = 2 × a × 125
100 - 225 = 250a
250a = -125
a = -125/250
a = -1/2

Now, we can find time duration by using the formula -
v = u + at
10 = 15 + (-1/2)t
1/2t = 15 - 10
1/2t = 5
t = 5 × 2
t = 10 sec.
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Hope it will help you...
Best of luck...

Thanks !!!
Regards - Pratik Ratna