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)

1 Answer
Apr 25, 2016

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+12gt2, inserting given values
ht=12×10t2=5t2 .....(1)

Let us find distance of flight in time t1
ht1=5(t1)2 .....(2)

It is given that displacement in tth second is 35 meters. Subtracting (2) from (1) and setting it equal to the given value.
htht1=5t25(t1)2=35, Simplifying and solving for t

5t25(t22t+1)=35
or (10t5)=35
t=4s

From (1)
ht=5×42
=80m