Answer:
a) t = 0.54 seconds
b) t = 8 seconds
Step-by-step explanation:
Given in the question the equation
h = 40t - 5t²
where h is height in meters
t is time in seconds
Time it took to reach 20 meters
20 = 40t - 5t²
-5t² + 40t - 20 = 0
by using quadratic formula for factorisation
t = (-b± √(b)² - 4(a)(c) ) / 2(a)
t = 0.54 (upward motion)
or
t = 7.46 (downward motion)
b) Time it took to reach the ground
at ground h = 0
So,
0 = 40t - 5t²
t(40 - 5t ) = 0
t = 0 (at starting point)
or
40 -5t = 0
5t = 40
t = 40 /5
t = 8 seconds
