Question

The height h, in metres, of a ball thrown from a cliff can be modelled by the function with the rule h(t) = 20+15t-5t^2, where t less than/equal to 0 is the time measured in seconds.

a) find the initial height of the ball
b) find the time at which the ball hits the ground

Thanks would be highly appreciated!

Answer 1

initial ----> t = 0
So what do you get when you replace t with 0 in
h(t) = 20 + 15t - 5t^2 ?

When it hits the ground, isn't the height zero?
0 = 20 + 15t - 5t^2
divide by -5
t^2 - 3t - 4 = 0
solve the quadratic using whatever method you know, make sure to reject
the negative value of t
( it factors, you should be able to see the factors in your head)