Question

A car travels with a uniform velocity of 20 m/s for 5 s. The brakes are then applied and the car is uniformly retarded. It comes to rest in next 8 s. A velocity – time graph for the above motion is given below. Use the graph to find the answers of the following questions:-
What is the acceleration caused by the car represented by section AB of the given graph?
a. 4 m/s2
b. 0.25 m/s2
c. 0
d. 2 m/s2

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Answer 1

Initial Velocity = 20 m/sec

Time = 5 seconds.

After 5 seconds

Initial velocity = 20 m/sec

Final velocity = 0m/sec

Time = 8seconds

(i) Distance covered in first 5 seconds

Since Body moved with uniform motion, this means that acceleration =0

So, From 2nd equation of motion :-

(ii) Distance covered after breaks are applied :-

U= 20 m/sec

V = 0 m/sec

T = 8 second

So,

v = u + at

a = v - u / t

a = -20/8

= - 2.5

So,

s = v^2 - u^2/2a

s = -20^2/-5

s = 80 m

(iii) Total Distance travelled

100 + 80 = 180 m

(iv)  Acceleration during 1st 5 seconds = 0m/sec²

      Acceleration during last 8 seconds = (-2.5)m/sec²

Answer 2

Answer:

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