From the top of a building 40 m tall, a boy projects a stone vertically upwards with an initial velocity 10 ms -1 such that it eventually falls to the ground. After how long will the stone ștrike the ground ? Take g=10 ms -2

Question

From the top of a building 40 m tall, a boy projects a stone vertically upwards with an initial velocity 10 ms -1 such that it eventually falls to the ground. After how long will the stone ștrike the ground ? Take g=10 ms -2 (A) 1 s (B) 2 s (C) 3 s (D) 4 s

Tardigrade Admin · Accepted Answer

S=u t+(1/2) g t2 or 40=-10 t+(10/2) t2 or t2-2 t-8=0 or (t+2)(t-4)=0 ⇒ t=4 s as t can't be negative.

Q. From the top of a building $40 m$ tall, a boy projects a stone vertically upwards with an initial velocity $10 m s^{- 1}$ such that it eventually falls to the ground. After how long will the stone ștrike the ground ? Take $g = 10 m s^{- 2}$

1 s

2 s

3 s

4 s

$S = u t + \frac{1}{2} g t^{2}$
or $40 = - 10 t + \frac{10}{2} t^{2}$
or $t^{2} - 2 t - 8 = 0$
or $(t + 2) (t - 4) = 0$
$\Rightarrow t = 4 s$ as $t$ can't be negative.

Q. From the top of a building 40m tall, a boy projects a stone vertically upwards with an initial velocity 10ms−1 such that it eventually falls to the ground. After how long will the stone ștrike the ground ? Take g=10ms−2

1 s

2 s

3 s

4 s

S=ut+21​gt2 or 40=−10t+210​t2 or t2−2t−8=0 or (t+2)(t−4)=0 ⇒t=4s as t can't be negative.

Q. From the top of a building $40 m$ tall, a boy projects a stone vertically upwards with an initial velocity $10 m s^{- 1}$ such that it eventually falls to the ground. After how long will the stone ștrike the ground ? Take $g = 10 m s^{- 2}$

$S = u t + \frac{1}{2} g t^{2}$
or $40 = - 10 t + \frac{10}{2} t^{2}$
or $t^{2} - 2 t - 8 = 0$
or $(t + 2) (t - 4) = 0$
$\Rightarrow t = 4 s$ as $t$ can't be negative.