If a stone is thrown vertically upward from the surface of the moon with a velocity of 9 m/s, its height (in meters) after t seconds is h = 9t − 0.83t2. (Round your answers to two decimal places.)

Question

(a) What is the velocity of the stone after 1 s?

(b) What is the velocity of the stone after it has risen 15 m?

Answer 1

h(t) = 9t - .83t^2

h(1) = 9 - .83 = 8.17 meters

15 = 9t - .83t^2

.83t^2 -9t + 15 = 0

use the quadratic formula

t = 9/1.66 +or - (1/1.66)sqr(81-4(.83)(15))

t =about 8.8 seconds to reach 15 meters on the way down

or about about 2.1 seconds to reach 15 m. on the way up