Question

A ball is thrown upward from the top of a tower 40 m high and velocity 10m/s. find the time taken to strike the ground

Answer 1

Answer:

t = 4s

Explanation:

u = 10m/s

a = -10m/s (due to downward direction)

s = -40m (at the point where stone strikes the ground)

using the equation, s = ut + 1/2 gt²

-40 = 10×t + 1/2 × (-10) × t²

-40 = 10t - 5t²

5t² - 10t - 40 = 0

On solving, we get

t = -2s or t = 4s

We take the positive value of t = 4s

Answer 2

$u=+10m/s, a=-10m/s^2$ and $s=-40m$

(at the point where stone strikes the ground)

Substituting in $s=ut+\frac{1}{2}at^2$ we have

$-40=10t+5t^2$

or $5t^2-10t-40=0$

or $t^2-2t-8=0$

Solving this, we have $t=4s$ and $-2s$. Taking the positive value $t=4s$.

#SPJ3