Question

Standing at the top of a 30.0 m high cliff, you throw a rock straight down with a velocity of 8.00 m/s. After how many seconds does it hit the ground?

Answer 1

It will take 1.789 sec

Step-by-step explanation:

We have given height h = 30 m

Initial velocity u = 8 m/SEC

Acceleration due to gravity
`g=9.8m/sec^2`

Now according to second equation of motion
`h=ut+(1)/(2)gt^2`
`30=8t+4.9t^2`

`4.9t^2+8t-30=0`

After solving we get t = -3.42 sec and t = 1.789 sec

As negative time is not possible so time will be 1.789 sec