Posted by **Tina** on Saturday, July 16, 2011 at 10:19pm.

A person standing near the edge of a cliff 120 feet above a lake throws a rock upward with an initial speed of 40 feet per second. The height of the rock above the lake at the bottom of the cliff is a function of time and is described by the function H(t) = –16t2 + 40t + 120.

a) How many seconds will it take until the rock reaches its maximum height?

b) What is that height?

- Math -
**Max**, Saturday, July 16, 2011 at 11:03pm
H(t) = -16t^2 + 40t + 120

Finding critical point...

H'(t) = -32t + 40 ...... Differentiation

0 = -32t + 40

32t = 40

t = 1.25 seconds

Thats you answer for (a). Use it to find the answer for (b).

- Math - typo -
**Max**, Saturday, July 16, 2011 at 11:04pm
Thats you...

I meant "that's your..."

## Answer this Question

## Related Questions

- Math - For this problem, a person standing on the edge of a cliff throws a rock ...
- physics - A person is standing 100 feet from a tall cliff. She throws a rock 80 ...
- Physics - A person, standing on a vertical cliff a height h above a lake, wants ...
- Math - A boy throws a stone into a lake from a 74 foot high wall. The chart ...
- physics - a boy stands on a cliff overlooking a lake below. He throws a rock at ...
- Math - Sarah throws rocks into a quarry lake from the top of a 67 foot high wall...
- Math - You toss a rock up vertically at an initial speed of 34 feet per second ...
- physics - A rock is thrown vertically upward from the edge of a cliff. The rock ...
- physics - A rock is thrown vertically upward from the edge of a cliff. The rock ...
- Math - You drop a rock off a bridge. The rock’s height, h (in feet above the ...