A ball is at height h(t)=15+10t−5t² metres. Find the positive time, in seconds, at which it reaches the ground.

Question

G1 Physics · Accepted Answer

Set h=0: 15+10t−5t²=0. Divide by −5 to get t²−2t−3=0=(t−3)(t+1). Roots are 3 and −1; the positive physical time is 3 s.