Time and distance

[estacey]

Hi, I just wanted to thank anyone who answers this and tries to help. It's for grade 11 math. I don't understand how to write the full solution.

A flare is fired vertically from the top of a platform so that its height, h, in meters, after t seconds is given by h= -5t^2+40t+3.
a) How high is the platform?
b) At what time is the flare at a height above 38m?
c) How long is the flare in the air?

Thanks!

 

[Deleted member 4993]

Hi, I just wanted to thank anyone who answers this and tries to help. It's for grade 11 math. I don't understand how to write the full solution.

A flare is fired vertically from the top of a platform so that its height, h, in meters, after t seconds is given by h= -5t^2+40t+3.
a) How high is the platform?
b) At what time is the flare at a height above 38m?
c) How long is the flare in the air?

Thanks!

a) How high is the platform?

Hint At t=0 - what is 'h'?

b) At what time is the flare at a height above 38m?

solve for 't from 38= -5t^2+40t+3

continue.....

 

[Romsek]

c) what determines "not being in the air".

Apply Subhotosh's suggestion for (b) with the appropriate height.

 

[Harry_the_cat]

Show us how you went with the hints!