Question

a body starts from rest and accelerates to attain a speed 72 km/h in 20 seconds then It retards to come to rest after covering a distance of 80 m. calculate the acceleration as well as the retardation of the body

Answer 1

u=0
v=72km/h=20m/sec
v=u+at
20=0+a×20
20a=20
a=1m/sec^2

Now
u=20m/sec
v=0
s=80m
2as=v^2 -u^2
2×a×80=-20×20
8a=-20
a=-2.5 m/sec^2

Answer 2

Hey!

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Initial velocity (u) = 0
Final velocity (v) = 72 km/h = 20 m/s
Time taken = 20 seconds
Distance travelled = 80 m
Acceleration = ?
Retardation = ?

We know,

v - u = at

20 - 0 = a × 20
20 = 20a
a = 1 m/s^2

Retardation -

u = 20 m/s
v = 0 (At last the body came at rest)
s = 80 m

We know,

v^2 - u^2 = 2as
0 - (20)^2 = 2 × a × 80
- 400 = 160 a
-400/160 = a
a = - 2.5 m/s^2


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Hope it helps...!!!