Question

A projectile thrown from the ground level at an angle of alpha, is vertically displaced 35 meters within the last one second before landing.How many meters might it have raised ? (Assume ;g=10 N/kg,There is no drag)

Answer 1

`80m`

Explanation:

As understood the problem.

Let `h` be the height from which the projectile starts its downward flight. Also let `t` be the time of downward flight. Let this point be origin.
As drag is to be ignored,
Kinematic equation is
`s=ut+1/2g t^2`, inserting given values
`h_t=1/2xx10 t^2=5t^2` .....(1)

Let us find distance of flight in time `t-1`
`h_(t-1)=5(t-1)^2` .....(2)

It is given that displacement in `t^(th)` second is 35 meters. Subtracting (2) from (1) and setting it equal to the given value.
`h_t-h_(t-1)=5t^2-5(t-1)^2=35`, Simplifying and solving for `t`

`5t^2-5(t^2-2t+1)=35`
or `(10t-5)=35`
`=>t=4s`

From (1)
`h_t=5xx4^2`
`=80m`