A body is thrown vertically upward at t = 0 . It is at a height 80,m at instants t₁ and t₂ . Als

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2.Motion in Straight Line

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A body is thrown vertically upward at $t = 0$ . It is at a height $80\,m$ at instants $t_1$ and $t_2$ . Also, it is at a height $60\,m$ at instants $t'_1$ and $t'_2$ . Then

A

$t_1 + t_2 = t'_1 + t'_2$

B

$t_1 + t_2 > t'_1 + t'_2$

C

$t_1 + t_2 < t'_1 + t'_2$

D

None of these

Solution

By using

$\mathrm{s}=\mathrm{ut}+\frac{1}{2} \mathrm{at}^{2}$ we have, $\mathrm{h}=\mathrm{ut}+\frac{1}{2}(-\mathrm{g}) \mathrm{t}^{2}$

$\Rightarrow \quad \mathrm{t}^{2}-\frac{2 \mathrm{u}}{\mathrm{g}} \mathrm{t}+\frac{2 \mathrm{h}}{\mathrm{g}}=0$

$\Rightarrow \mathrm{t}_{1}+\mathrm{t}_{2}=\frac{2 \mathrm{u}}{\mathrm{g}}$ Which is same for both.

Standard 11

Physics

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