Question

A model rocket is launched off the top of a platform. The height of the rocket is given by the function h(t) = -4.9t2+ 86t + 2.1, where h(t) is the height in meters and t is the time in seconds. When will the rocket's height be 200m?

Answer 1

t = 14.82 and 2.72secs

Explanation:

Given the function of the rocket height expressed as;

h(t) = -4.9t^2+ 86t + 2.1

if the rocket height is at 200m, then;

200 = -4.9t^2+ 86t + 2.1

multiplying through by 10

2000 = -49t^2 + 860t + 21

49t^2 - 860t - 21 + 2000 = 0

49t^2 - 860t + 1979 = 0

Factorize

t = 860±√(860)²-4(49)(1979)/2(49)

t = 860±√739,600-387,884/98

t = 860±√351,716/98

t = 860±593.06/98

t = 860+593.05/98 and 860-593.05/98

t = 1,453.05/98 and 266.94/98

t = 14.82 and 2.72secs

These are the times