MCQ
A ball is projected from top of a tower with a velocity of $5\,\, m/s$ at an angle of $53^o$ to horizontal. Its speed when it is at a height of $0.45 \,\,m$ from the point of projection is ........ $m/s$
- A$2$
- B$3$
- ✓$4$
- Ddata insufficient.
✓
Answer
Correct option: C.
$4$
c
According to conservation principle of machenic energy
According to conservation principle of machenic energy
$\mathrm{U}_{\mathrm{i}}+\mathrm{T}_{\mathrm{i}}=\mathrm{U}_{\mathrm{f}}+\mathrm{T}_{\mathrm{f}}$
$0+\frac{1}{2} \mathrm{mu}^{2}=\mathrm{mgh}+\frac{1}{2} \mathrm{mv}^{2}$
$\mathrm{u}^{2}=2 \mathrm{gh}+\mathrm{v}^{2}$
$\mathrm{v}=\sqrt{\mathrm{u}^{2}-2 \mathrm{gh}}$
$\mathrm{v}=\sqrt{5^{2}-2 \times 10 \times 0.45}$
$\mathrm{v}=\sqrt{25-9}=\sqrt{16}$
$\Rightarrow \quad \mathrm{v}=4 \mathrm{m} / \mathrm{s}$
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