Gujarati
Hindi
2.Motion in Straight Line
medium

A ball is dropped from the top of a building $100\,m$ high. At the same instant another ball is thrown upwards with a velocity of $40\,m / s$ from the bottom of the building. The two balls will meet after $..........\,s$

A

$3$

B

$2$

C

$2.5$

D

$5$

(AIIMS-2016)

Solution

(c)

Let balls meet after $t s$. The distance travelled by the ball coming down is

$s_1=\frac{1}{2} g t^2$

Distance travelled by the other ball

$s_2=40 t-\frac{1}{2} g t^2$

$\because \quad s_1+s_2=100\,m$

$\therefore \quad \frac{1}{2} g t^2+40 t-\frac{1}{2}\,g t^2=100\,m$

$t=\frac{100}{40}=2.5\,s$

Standard 11
Physics

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