Linear-Quadratic Systems

[ashley_sagaert]

a daredevil jumps off the CN tower and falls freely for several seconds before releasing his parachute. his height, h(t), in metres, t seconds after jumping, can be modelled by
h1(t)= -4.9t^ + t + 360 before he released his parachute; and
h2(t)= -4t + 142 after he released his parachute.
How long after jumping did the daredevil release his parachute?

 

[skeeter]

-4.9t² + t + 360 = -4t + 142

-4.9t² + 5t + 218 = 0

use the quadratic formula to solve for t ... choose the solution that makes sense for the problem.

 

[ashley_sagaert]

The thing is i don't know how to solve with the quadratic formula, could you complete the question so that i can kind of figure out how to solve my other questions, thank you very much
ashley

i do get the part that you explained but i don't get how to solve what follows that

 

[stapel]

i don't know how to solve with the quadratic formula, could you complete the question so that i can kind of figure out how to solve my other questions

If you don't know how to solve quadratic equations, then seeing one worked example isn't going to make any sense. You need to study and learn, before the solution would be helpful (even were we to provide such, and legitimate tutors generally don't).

Fortunately, there are loads of great lessons available online:

. . . . .Google results for "solving quadratic equations"

. . . . .Google results for "Quadratic Formula"

Once you have studied some lessons (at least two from each link!), please attempt the solving. If you get stuck, please reply showing how far you have gotten.

Thank you!

Eliz.

 

[Deleted member 4993]

a daredevil jumps off the CN tower and falls freely for several seconds before releasing his parachute. his height, h(t), in metres, t seconds after jumping, can be modelled by
h1(t)= -4.9t^2 + t + 360 before he released his parachute; and
h2(t)= -4t + 142 after he released his parachute.
How long after jumping did the daredevil release his parachute?

I have slightly different interpretation of the problem (compared to skeeter)

The parachute is opened at t=0 (for the parachute) at a height = h_2(t) = -4*0+142 = 142

So for free fall occurred for 142 ft.

Thus

for total time of free fall

-4.9*t^2 + t + 360 = 142

for total time of "parachute fall"

0 = - 4*t + 142