The height of a body above the ground is h(t)=20t-5t² m. Ignoring the launch instant t=0, when does it return to the ground?
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The height of a body above the ground is h(t)=20t−5t² m. Ignoring the launch instant t=0, when does it return to the ground?

G1 Physics · Accepted Answer

At ground level h=0: 20t−5t²=5t(4−t)=0. The roots are t=0 and t=4 s. t=0 is the launch instant, so the return time is 4 s.