Equations and Inequalities

1

1038373daj

New member
Joined
Sep 8, 2010
Messages
2
Applications:

Question: Height of a projectile: The height of an object thrown upward from the roof of a building 408 ft. tall, with an initial velocity of 96ft/sec. is given by the equation h- -16t^2 + 96t + 408, where h represents the height of the object after t seconds. How long will it take the object to hit the ground? Answer in exact form and decimal form rounded to the nearest hundredth.

Answer: t= 6 + the square root of 138 over 2 sec, t approx = 8.87 sec.

Work so far:

h= -16t^2 + 96 +408
a = -16
b= 96
c= 408

Equation used to solve problem x = - b square root b^2 - 4 (a)(c) over 2(a)

h= -96 square root 96^2 - 4 (-16)(408) over 2(-16)

h= 96 square root of 9216 - 26112 over -32

I'm stuck, im obviously on the wrong path, but i don't know where i went wrong, please help! Also i couldn't find a square root sign so every time it was in the problem i just wrote it out as you can see above, is there an option to put the symbol in to make it easier for you to understand?

Need help asap! Thank You!
Regards, Danielle
 
Question: Height of a projectile: The height of an object thrown upward from the roof of a building 408 ft. tall, with an initial velocity of 96ft/sec. is given by the equation h- -16t^2 + 96t + 408, where h represents the height of the object after t seconds. How long will it take the object to hit the ground? Answer in exact form and decimal form rounded to the nearest hundredth.

Answer: t= 6 + the square root of 138 over 2 sec, t approx = 8.87 sec.

Work so far:

h= -16t^2 + 96 +408
a = -16
b= 96
c= 408

Equation used to solve problem x = - b square root b^2 - 4 (a)(c) over 2(a)

h= -96 square root 96^2 - 4 (-16)(408) over 2(-16)

h= 96 square root of 9216 - 26112 over -32

I'm stuck, im obviously on the wrong path, but i don't know where i went wrong, please help! Also i couldn't find a square root sign so every time it was in the problem i just wrote it out as you can see above, is there an option to put the symbol in to make it easier for you to understand?
Click to expand...

Hi, Danielle,

You’re off to a fair start with “h= -96 square root 96^2 - 4 (-16)(408) over 2(-16)”, except it’s not h you are solving for, but t. “h” is equal to zero when the object reaches the ground. Also, watch your signs when multiplying negative numbers. One option is to replace the square root with a power of “.5”. Write it like this:

t = [-96 +/- (96^2 – 4(-16)(408))^.5]/(-32)
t = [-96 +/- (9216 + 26112)^.5]/(-32)
t = [-96 +/- 187.96]/(-32)

We get two answers, one positive and one negative. Choose the positive answer for this “real world” situation. (The negative answer would not make sense.)

t = 8.87 s (approx.)
 
You must log in or register to reply here.
Top