Question

marks:
Q.1 A constant retarding force of 50 Nis
applied to a body of mass 20 kg moving
initially with a speed of 15 m/s. The time
taken by the body to stop is: *​

Answer 1

Given :-

• Force (F) = 50N
• Mass (m) = 20kg
• Initial velocity (u) = 15m/s
• Final velocity (v) = 0

To find :-

• Time taken to stop

Solution :-

As we know that

→ Force = mass × acceleration

→ 50 = 20 × a

→ a = 50/20

→ a = 2.5m/s²

Acceleration of body becomes negative due to retardation.

Therefore, acceleration of body is -2.5m/s².

Now, according to first equation of motion

→ v = u + at

→ 0 = 15 + (-2.5) × t

→ 2.5t = 15

→ t = 15/2.5

→ t = 6s

Hence,

• Time taken to stop a body is 6s

Note :-

• s = ut + ½ at² (second equation of motion)
• v² = u² + 2as (third equation of motion)

Answer 2

$\star\:\:\:\bf\large\underline\blue{Given:—}$

☛︎ Force, F = 50 N

☛︎ Mass, m = 20 kg

☛︎ Initial velocity, u = 15 m/s

$\star\:\:\:\bf\large\underline\blue{To\:find:—}$

How long does the body take to stop ?

$\star\:\:\:\bf\large\underline\blue{Solution:—}$

From Newton's second law,we know that

$\boxed{\bf{\red{★ F=ma}}}$

↦50 = 20 × a m/s

↦a = 2.5 m/s

Now,

as per first equation of motion:-

$\boxed{\bf{\green{★ v=u+at}}}$

↦0 = 15 + (-2.5)×t

↦t = 15/2.5

$\boxed{\bf{\purple{t=6\:s}}}$

Hence, the time taken by the body to stop is 6 seconds.

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