Question 38318
A. how high is the ball after 3 seconds
{{{h=70(3)-5(3)^2}}}
{{{h=210-45}}}
{{{h=165}}}
B. after how many seconds will the ball be 169 meters high
{{{169=70(t)-5(t)^2}}}
{{{-5(t)^2+70t-169=0}}}
't' is either {{{(-70 + (1520)^(1/2))/(-10))}}} or {{{(-70 - (1520)^(1/2))/(-10))}}}
The answer is {{{(-70 - (1520)^(1/2))/(-10))}}} because you can not have a negative time. The answer is about 10.8987
C. when will the ball hit the ground?
{{{0=70(t)-5(t)^2}}}
{{{0=t(70-5t)}}}
set to zero (use product property)
t=0
70-5t=0
-5t=-70
t=14
The ball will hit the ground after 14 seconds.