Question

Question 5.5 A constant retarding force of 50 N is applied to a body of mass 20 kg moving initially with a speed of 15 ms–1. How long does the body take to stop?

Chapter Laws Of Motion Page 110

Answer 1

ANSWER
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Force = Mass × Acceleration
- 50 N = 20 kg × Acceleration

=> Acceleration = 50/20
=> Acceleration = 5/2 m/sec ^2

Initial velocity = 15 m/sec
Final velocity = 0 { at rest }
Acceleration = 5/2

Using first equation of motion

v = u + at
In case of retardation
v = u - at

0 = 15 - 5/2t
-15 = 5/2 t
t = 15 × 2/5
t = 6

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ANSWER = 6 SECONDS
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HOPE IT HELPS :):):):):):):):):)

Answer 2

Magnitude Regarding force = 50N
hence, regarding force = -50N
Mass of body = 20 Kg
Intial speed = 15 m/s

First find retardation ,
We know,
F = ma
-50 = 20 × a
a = -2.5 m/s²

Now , use kinematics equation ,
V = U + at
Finally body takes rest .so, V = 0
0 = 15 + (-2.5)t
15 = 2.5t
t = 15/2.5 = 6sec