A horizontal bridge is built across a river. A student standing on the bridge throws a small ball vertically upwards with a velocity 4   m   s - 1 . The ball strikes the water surface after 4   s . The height of bridge above water surface is (Take g = 10   m   s - 2 ):

Step-by-step solution

The formula to calculate the vertical height travelled by the ball is given by H = u t - 1 2 g t 2       . . . 1 Substitute the values of the known parameters into equation (1) to calculate the required height. H = 4   ms - 1 × 4   s - 1 2 × 10   ms - 2 × 4   s 2 = - 64   m Hence, the required height of the bridge above the surface of the river is 64   m .