Thread: word problem help

Hi, can someone help me with this? I don't even know how to set up the equation.

If an object is propelled upward from a height of 96 feet at an initial velocity of 80 feet per second, then its height h after t seconds is given by the equation h = - 16t2 + 80t + 96. After how many seconds does the object hit the ground?

You already have the necessary equation: . Hitting the ground means the height at which the object is is : where is the time it hits the ground (assuming it gets launched at ).

Originally Posted by EandH

Hi, can someone help me with this? I don't even know how to set up the equation.

If an object is propelled upward from a height of 96 feet at an initial velocity of 80 feet per second, then its height h after t seconds is given by the equation h = - 16t2 + 80t + 96. After how many seconds does the object hit the ground?

as this is the height equation,
then when the ball first hits the ground, the height will be zero.
If you write the equation as a multiplication (factorise), the answer will be in one of the factors.





This is zero for t=6 seconds and t=-1 second.
The t=-1 comes from the graph which can show times "preceding" when the ball was propelled!!

Hence the answer is 6 seconds.

Thanks for your help!