a flare is fired upwards from the deck of a chip. The flar hits the water. The height of the flare, h, in metres, above the water t seconds is given by the function h= -4.9t^2 + 98t + 8
a. How long does it take the flare to hit the water?
b.How high is the deck of the ship above the water?
I calculated the height of the flare as 498m through completing the square, and i calculated the time to reach maximum height as 10 seconds. But now I'm stuck.
Can anyone help me plz!!
I presume you are saying you don't know how to solve the quadratic.
When all else fails, use the quadratic formula:
For this problem we have that a = -9.8, b = 98, and c = 8.
You will have two answers as a result for the time. One of these will be negative, and thus is an unphysical solution and may be discarded.
-Dan
I think you have made the question more complicated then it actually is (i think meaning that i may be in the wrong)
a) How long does it take to reach the water i.e. h = 0
-4.9t^2+98t+8 = 0
t = (-98+squareroot(98^2-(4*-4.9*-8))/(2*-4.9),
t = (-98-squareroot(98^2-(4*-4.9*-8))/(2*-4.9)
t = -0.08130215107
t = 20.08130215, therefore time to reach 0 metres i.e. water, i 20.08130215 seconds as time cant be negative.
b) How high is the Deck? Just use t = 0 seconds i.e. the flare hasnt left the deck yet.
h = -4.9(0^2)+98(0)+8
h = 8m
I think this is right, someone please correct me if im wrong.
Hope this helps, Sean.