Saturday

April 19, 2014

April 19, 2014

Posted by **trellis** on Tuesday, June 5, 2007 at 6:04pm.

Two ways to find it.

1) AT the top, max height, will be one half of the time it would come back down and hit the earth at h=0

0=-15t^2+60t solve for t.

Then divide that by two.

2) At max height, the change in height/per time is zero.

dh/dt= -30t+60

set that to zero, and solve for t.

If you dont know derivatives yet, forget this method.

If object is thrown upward with an intitial velocity of 15 ft per second, then its height is given by h=-15t^2 + 60t. What is the maximum height?

The time to reach maximum height is given by Vf = Vo - gt where Vf = the final velocity, Vf = 0, Vo = the initial velocity, g = acceleration due to gravity, ~32), and t = the time.

Therefore, 0 = 15 - 32t making t = .46876 sec. sec.

The height reached is given by h = Vot - 16t^2. You give an equation of h = 60t - 15t^2 implying that Vo = 60, not 15, and g = 30, not 32.

Using your equation, h = 60(.46875) - 15(.46875)^2 = 24.829 ft. ft.

Using the initial velocity stated, h = 15(.46875) - 15(.46875)^2 = 3.735 feet.

If the real initial velocity is 15 fps, then 60 does not belong in the equation for height, rather 15 instead..

I believe this result derives from using the wrong value for g which should be 16.

Using g == 16 and the correct V0 = 15 in the equation for height, we get

0 = 15 - 16t making t = ..9375 sec.

Then, h = 15(.9375) - 16(.9375)^2 = 14.0625 - 14.0625 = 0.

This leads to h = 15(1) - 15(1) = 0

Therefore, with Vo = =15

**Related Questions**

Algebra 2 - If an object is thrown vertically upward with an initial velocity of...

Algebra - If an object is thrown vertically upward with an initial velocity of ...

Math - The height(h) of an object that has been dropped or thrown in the air is...

math - The height of an object thrown upward with an initial velocity of 96 feet...

college algebra - The height of an object thrown upward with an initial velocity...

Math - The height(H) of an object that has been dropped or thrown in the air is ...

algebra - a stone is thrown up from a height of 30 ft. The initial velocity is ...

Algebra - A ball is thrown into the air with an upward velocity of 28 ft/s. Its...

algebra - A ball is thrown into the air with an upward velocity of 28 ft/s. Its ...

Algebra 2 - If an object is thrown vertically upward with an initial velocity of...