Question

A stone is thrown vertically upward from ground level with speed of 25m/s. At what time is it 5m above the ground.​

Answer 1

The stone will be
`5m` above the ground in
`2.3s`

Step-by-step explanation:

As the stone is thrown vertically upward from ground with speed i.e.,

the initial velocity,
`u=25m/s`,

the final velocity,
`v=0m/s`,

acceleration due to gravity,
`a = -10m/s^2` (upward motion)

`v=u+at\\0=25+(-10)t\\0=25-10t\\t=2.5s`

To calculate the height at which the stone reached above the ground we can use the below formula:

`s=ut+(1)/(2)at^2`

`s=25*2.5+(1)/(2)(-10)(2.5)^2`

`s=62.5-5*6.25=62.5-31.25=31.25m`

Now, the time taken by stone to reach
`5m` above the ground can be calculated using

`u=0m/s\\s=31.25-5=26.25m\\a=10m/s^2\\t=?`

`s=ut+(1)/(2) at^2\\`

`26.25=0 * t+(1)/(2) * 10 * t^2`

`26.25=0+5t^2`

`5t^2=26.25`

`t^2=(26.25)/(5)=5.25`

`t=√(5.25) =2.3s`

Thus, at
`2.3s` the stone will reach
`5m` above the ground.