A body is dropped from a certain height h ( h is very large) and second body is thrown downward with

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2.Motion in Straight Line

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A body is dropped from a certain height $h$ ( $h$ is very large) and second body is thrown downward with velocity of $5 \,m / s$ simultaneouly. What will be difference in heights of the two bodies after $3 \,s$ is ....... $m$

A

$5$

B

$10$

C

$15$

D

$20$

Solution

(c)

$u_{\text {rel }}=u_1-u_2=0-(-5)=5 ms ^{-1}$

$t=3 \,s$

$a_{ rel }=a_1-a_2=-g-(-g)=0 \,ms ^{-2}$

$s_{ rel }=u_{ rel } t+\frac{1}{2} a_{ rel } t^2$

$\Rightarrow s_{ rel }=5 \times 3=15 \,m \quad\left(\because a_{ rel }=0\right)$

So, $s_{\text {rel }}=15 \,m$

Standard 11

Physics

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