# An object is thrown vertically from a height of 2 m at 4 m/s. How long will it take for the object to hit the ground?

Apr 17, 2017

1.4 Sec

#### Explanation:

We know when it attains maximum height it Final velocity will be zero .
so ,
from eq. $v = u + a \cdot t$

time taken to attain maximum height is =$\frac{- u}{a}$(for this case)
which is =$\frac{- 4}{-} 10 = 0.4 \sec$ $\text{------------(1)}$

now distance traveled upward $\implies$
$S = u t + \frac{1}{2} a {t}^{2}$$\text{--------(2)}$

we get
$S = 4 \cdot 0.4 + \frac{1}{2} \cdot \left(- 10\right) \cdot {\left(0.4\right)}^{2} = 0.8 m$

now it again falls from that height to ground which is $2.0 + 0.8 = 2.8 m$

now time taken to hit the ground is taken by eq 2$\implies$
$2.8 = \frac{1}{2} \cdot 10 \cdot {t}^{2} = 0.74 \sec$

so we will add (1) and (2) to get our answer we get=$0.4 + 0.74 = 1.4 \sec$