4-1.Newton's Laws of Motion
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$15\, m s ^{-1}$ की आरंभिक चाल से गतिशील $20\, kg$ संहति के किसी पिण्ड पर $50\, N$ का स्थाई मंदन बल आरोपित किया गया है। पिण्ड को रूकने में कितना समय लगेगा ?

A

$6$

B

$5$

C

$3$

D

$8$

Solution

Retarding force, $F=-50 \,N$

Mass of the body, $m=20 \,kg$

Initial velocity of the body, $u=15 \,m / s$

Final velocity of the body, $v=0$

Using Newton's second law of motion, the acceleration ( $a$ ) produced in the body can be calculated as:

$F=m a$

$-50=20 \times a$

$\therefore a=\frac{-50}{20}=-2.5 \,m / s ^{2}$

Using the first equation of motion, the time ( $t$ ) taken by the body to come to rest can

be calculated as: $v=u+a t$

$\therefore t=\frac{-u}{a}=\frac{-15}{-2.5}=6\;s$

Standard 11
Physics

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