if an object is propelled upward from a height of s feet at an initial velocity of v feet per second, then its height h after t seconds is given by the equation h=-16t^2+vt+s where h is in feet. If the obct is propelled from a height of 12 feet with an initial velocity of 64 feet per second, its height h is given by the equation h=-16t^2+64+12 after how many seconds is the height 72 feet?

Question

kinggeorge · Answer

All you need to do for this, is set $h=72$. So you have the equation$$72=-16t^2+64t+12$$Simplifying a little bit, we have$$16t^2-64t+60=0$$Dividing by 4, we get$$4t^2-16t+15=0.$$Once you're here you just need to fact the quadratic polynomial (either by inspection or using the quadratic formula). Can you do that yourself?

anonymous · Answer

Yes Yes I can, thank you so much :)

kinggeorge · Answer

Excellent. Let me know if you get stuck.

anonymous · Answer

Ok I will

anonymous · Answer

I got 3/2 and 5/2

kinggeorge · Answer

Looks perfect to me. Nice job.