After his final exam, a student goes to the top of a building and throws his book into the air. The height h in feet of the book above the ground is given by: h = −16t 2 + 32t + 128. How long is the book in the air?

Question

After his final exam, a student goes to the top of a building and throws his book into the air. The height h in feet of the book above the ground is given by: h = −16t 2 + 32t + 128. How long is the book in the air?

anonymous · Answer

ur given the height function,differentiate it wrt t and get the time at which it'll reach the maximum height... and that'll be at t=1 sec.
at this the height is 144. so now u need to calculate the time required by the book to reach the ground. so 144=5t^2 => t=12/sqrt(5).
so the total time is 1+12/sqrt(5).
remember i've done this with the assumption that wen he throws book into air, it finally reaches ground.
note: the height of the building is t=0,h=128.

anonymous · Answer

6 seconds?