A stone is dropped from a bridge at a height of 180 m over a river. After 3 second, a second ball is thrown straight downwards. What should be the initial velocity of the second ball so that both hit the water simultaneously?

Question

A stone is dropped from a bridge at a height of 180 m over a river. After 3 second, a second ball is thrown straight downwards. What should be the initial velocity of the second ball so that both hit the water simultaneously? (A) 45 m / s (B) 46 m / s (C) 50 m / s (D) 55 m / s

Tardigrade Admin · Accepted Answer

When stone is dropped S =(1/2) gt 2 180=(1/2) × 10 × t 2 t=6 seconds Second ball is taking 3 second to reach the river 180= u × 3+(1/2) × 10 × 9 ⇒ 180= u × 3+5 × 9 u =(180-45/3)=45 m / s

Q. A stone is dropped from a bridge at a height of $180 m$ over a river. After $3$ second, a second ball is thrown straight downwards. What should be the initial velocity of the second ball so that both hit the water simultaneously?

45 m / s

46 m / s

50 m / s

55 m / s

When stone is dropped $S = \frac{1}{2} g t^{2}$
$180 = \frac{1}{2} \times 10 \times t^{2}$
$t = 6$ seconds
Second ball is taking $3$ second to reach the river
$180 = u \times 3 + \frac{1}{2} \times 10 \times 9 \Rightarrow 180 = u \times 3 + 5 \times 9$
$u = \frac{180 - 45}{3} = 45 m / s$

Q. A stone is dropped from a bridge at a height of 180m over a river. After 3 second, a second ball is thrown straight downwards. What should be the initial velocity of the second ball so that both hit the water simultaneously?