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

• Dec 7th 2011, 03:04 PM
bashemgud
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
• Dec 7th 2011, 03:18 PM
mr fantastic
Re: help with 2 word problems - factoring
Quote:

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.
• Dec 7th 2011, 03:28 PM
bashemgud
Re: Value of h=48t-16t^2 when t = 2 and t = 2.5.
so 2.0 secs is 32feet and 2.5 is 20 feet?

for some reason it seems backwards to me.
• Dec 7th 2011, 03:31 PM
Quacky
Re: Value of h=48t-16t^2 when t = 2 and t = 2.5.
This is because after 1.5 seconds, the rocket is descending.
• Dec 7th 2011, 03:31 PM
mr fantastic
Re: Value of h=48t-16t^2 when t = 2 and t = 2.5.
Quote:

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.
• Dec 7th 2011, 03:51 PM
bashemgud
Re: Value of h=48t-16t^2 when t = 2 and t = 2.5.
Thanks everyone.