Question

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?

Answer 1

1.4 Sec

Explanation:

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

time taken to attain maximum height is =`(-u)/a`(for this case)
which is =`(-4)/-10=0.4 sec` `"------------(1)"`

now distance traveled upward `=>`
`S=ut+1/2at^2` `"--------(2)"`

we get
`S=4*0.4+1/2*(-10)*(0.4)^2=0.8 m`

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

now time taken to hit the ground is taken by eq 2`=>`
`2.8=1/2*10*t^2=0.74 sec`

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