A man throws a ball vertically upward and it rises through 20 m and returns to his hands. What was the initial velocity (u) of the ball and how much time (T) is remained in the air? (Take g = 10 m s-2)

Question

A man throws a ball vertically upward and it rises through 20 m and returns to his hands. What was the initial velocity (u) of the ball and how much time (T) is remained in the air? (Take g = 10 m s-2) (A) u = 10 m s-1, T = 2 s (B) u = 10 m s-1, T = 4 s (C) u = 20 m s-1, T = 2 s (D) u = 20 m s-1, T = 4 s

Tardigrade Admin · Accepted Answer

Taking vertically upward motion of ball, we have

υ^{2} = u^{2} + 2 g s

or

0 = u^{2} + 2 \times (- 10) \times 20

or

u = 20 m s^{- 1}

Taking vertical motion of ball for whole flight,

S = u t + \frac{1}{2} g t^{2}

0 = 20 \times t + \frac{1}{2} \times (- 10) \times t^{2}

5 t^{2} - 20 t = 0 \Rightarrow t = 4 s .

Q. A man throws a ball vertically upward and it rises through 20 m and returns to his hands. What was the initial velocity (u) of the ball and how much time (T) is remained in the air? (Take $g = 10 m s^{- 2}$ )

$u = 10 m s^{- 1}, T = 2 s$

$u = 10 m s^{- 1}, T = 4 s$

$u = 20 m s^{- 1}, T = 2 s$

$u = 20 m s^{- 1}, T = 4 s$

Q. A man throws a ball vertically upward and it rises through 20 m and returns to his hands. What was the initial velocity (u) of the ball and how much time (T) is remained in the air? (Take g=10ms−2)

u=10ms−1,T=2s

u=10ms−1,T=4s

u=20ms−1,T=2s

u=20ms−1,T=4s

Taking vertically upward motion of ball, we have υ2=u2+2gs or 0=u2+2×(−10)×20 or u=20ms−1 Taking vertical motion of ball for whole flight, S=ut+21​gt2 0=20×t+21​×(−10)×t2 5t2−20t=0⇒t=4s.

Q. A man throws a ball vertically upward and it rises through 20 m and returns to his hands. What was the initial velocity (u) of the ball and how much time (T) is remained in the air? (Take $g = 10 m s^{- 2}$ )

$u = 10 m s^{- 1}, T = 2 s$

$u = 10 m s^{- 1}, T = 4 s$

$u = 20 m s^{- 1}, T = 2 s$

$u = 20 m s^{- 1}, T = 4 s$