First slide

Vertical projection from ground

Question

A body of mass 1kg is projected upward with a speed of 10 m/s. It returns to the point of projection with a speed of 8 m/s. Air resistance remains constant during the entire Journey of the body. Then maximum height attained by the body is ____

Moderate

A

4.1 m
B

3.2 m
C

5 m
D

6.2 m

Solution

Let ‘R’ be the average resistance offered by air.
$\begin{array}{l} ∴ 2 R H = \frac{1}{2} m u^{2} - \frac{1}{2} m v^{2} ........ (1) \\ A l s o, u^{2} = 2 (g + \frac{R}{m}) H ......... (2) \\ S o l v i n g, H = \frac{v^{2} + u^{2}}{4 g} = \frac{8^{2} + 10^{2}}{4 \times 10} m = 4.1 m \end{array}$

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