Askiitians Expert Ankit -BVCOE
Last Activity: 14 Years ago
please check the image provided also.
When we say 100 feet from ground we should also check that the rocket is already 72 feet above the ground.
so the relative height rocket must reach to attain 100 ft from ground is actually 18 feet.
so the equation has been modified to
so now height(h) can be taken as 18 feet.
-16t^2 + 64t +72 >= 18
=> -16t^2 +64t +54 >=0
which is reduced to 8t^2 -32t -27 >=0
for time > 5 sec this equation is positive .
SO we can say that after time= 5 sec , the rocket will be above 100 feet of height above ground.
PS: there might be some printing error in equation as it is giving only one valid value of time.