Question

A baseball player hits a pitched ball when it is 4 ft above the ground. The initial upward velocity is 80 ft/s. How

long will it take for the ball to hit the ground?

Answer 1

t=+4.06

Explanation:

when the baseball hits the ground, the height will be 0.

h=0we are given that h=−16t2+64t+4.

this means that the height is 0 when −16t2+64t+4=0.−16t2+64t+4=0divide both sides by 4:−4t2+16t+1=04=0−4t2+16t+1=0 can be solved using the quadratic formula:t=−b±√b2−4ac2a, where at2+bt+c=0.at2+bt+c=−4t2+16t+1a=−4,b=16,c=1t=−b+√b2−4ac2aor−b−√b2−4ac2a−b+√b2−4ac2a=−16+√272−8=−0.06..−b−√b2−4ac2a=−16−√272−8=4.06 (3s.f.)we have 2 values for t:−0.06 and 4.06.

since time cannot be negative, only the positive value can be taken.

this is 4.06, to 3 significant figures.the time taken is 4.06 seconds.