Question

a stone is thrown horizontally with an initial speed of 30 m/s from a bridge. fins the stone's total speed when it enters the water 4 seconds later, assuming that air resistance is negligible

Answer 1

The stone is thrown horizontally, after throwing the stone experiences an acceleration of g along the -ve veritcal direction (down direction is -ve). It is said that it enters water after 4 seconds. Since there is no decceleration along the horizontal direction (air resistance is neglected), the horizontal velocity of the stone will remain constant, Therefore after 4 seconds the horizontal velocity of the stone will be,

V_h = 30m/s

In the vertical direction, the stone has a initial velocity of 0 (since the stone is thrown horizontally) and it is experiencing an acceleration of -g, Therefore we can calculate final velocity by the equation,

(-ve because it is in downward direction). Therefore the magnitude of total velocity of the stone after 4 seconds is,