+0

# need help

0
75
3

The equation y = -4.2t^2 + 42t + 18.9 describes the height (in meters) of a ball tossed up in the air at 42 meters per second from a height of 18.9 meters from the ground, as a function of time in seconds. In how many seconds will the ball reach maximum height?

Feb 1, 2022

#1
+1334
+3

The maximum value is $$18.9 - {1764\over-16.8} = 123.9$$. Subsitute the equation like this:$$123.9=-4.2t^2+42t+18.9$$. Solve for $$t$$, and you get $$\color{brown}\boxed 5$$

Feb 1, 2022
#2
+117100
+2

The equation y = -4.2t^2 + 42t + 18.9 describes the height (in meters) of a ball tossed up in the air at 42 meters per second from a height of 18.9 meters from the ground, as a function of time in seconds. In how many seconds will the ball reach maximum height?

This is a concave down parabola, the max will be when t = axis of symmetry

max height will be reached when t = -42/-8.4 = 5seconds

Feb 1, 2022
edited by Melody  Feb 1, 2022
#3
+1334
+1

The x-value of the vertex can be also be found by doing $$-b\over2a$$, in a quadratic equation with the format $$a^2 + bx + c = 0$$.

This also yields $$\color{brown}\boxed5$$

BuilderBoi  Feb 1, 2022
edited by BuilderBoi  Feb 1, 2022