Question

A stone is thrown with an initial speed of 4.9 m/s from a bridge in vertically upward direction. It falls down in water after 2 sec. The height of the bridge is

• A. 4.9 m
• B. 9.8 m
• C. 19.8 m
• D. 24.7 m

Answer 1

Answer: (B)

9.8 m

Answer 2

Speed of stone in a vertically upward direction is 4.9 m/s. So for vertical downward motion we will consider $u = - 4.9\mspace{6mu} m/s$

$h = ut + \frac{1}{2}gt^{2} = - 4.9 \times 2 + \frac{1}{2} \times 9.8 \times (2)^{2} = 9.8\mspace{6mu} m$