Thread: Value of h=48t-16t^2 when t = 2 and t = 2.5.

The two questions are similar but I keep getting way different answers

A water rocket is launched upwards with an initial velocity of 28 ft/sec. Its height H in feet after t seconds is given by h=48t-16t^2. Determine the height of the rocket after 2.5 secs after it has been launched.

The second question is the same, but 2.0 secs after launch

Thanks so much guys

Originally Posted by bashemgud

The two questions are similar but I keep getting way different answers

A water rocket is launched upwards with an initial velocity of 28 ft/sec. Its height H in feet after t seconds is given by h=48t-16t^2. Determine the height of the rocket after 2.5 secs after it has been launched.

The second question is the same, but 2.0 secs after launch

Thanks so much guys

Substitute t = 2.5 and t = 2 into h=48t-16t^2 and do the arithmetic.

so 2.0 secs is 32feet and 2.5 is 20 feet?

for some reason it seems backwards to me.

This is because after 1.5 seconds, the rocket is descending.

Originally Posted by bashemgud

so 2.0 secs is 32feet and 2.5 is 20 feet?

for some reason it seems backwards to me.

Your answers are correct but your discomfort with them is concerning. I suggest you review parabolas and their graphs.

Thanks everyone.