For a distance, dd, an initial velocity, v_0v0, an acceleration of aa, and a time of tt
color(white)("XXX")d=v_0t+at^2XXXd=v0t+at2
In this case
color(white)("XXX")d=-2 " m"XXXd=−2 m (2 meters below the height from with it was thrown)If it was dropped and not thrown up there would be no negative sign
color(white)("XXX")v_0= 2 " m"/"sec"XXXv0=2 msec
color(white)("XXX")a=-9.8 " m"/(sec"^2)XXXa=−9.8 msec2 (standard gravity assumed)
So we have
color(white)("XXX")-2.0" m" = 2.0t " m" + (-9.8t^2)" m"XXX−2.0 m=2.0t m+(−9.8t2) m
color(white)("XXX")98t^2-20t-20=0XXX98t2−20t−20=0
Using the quadratic formula:
color(white)("XXX")t=(20+-sqrt(20^2-4(98)(-20)))/(2(98))XXXt=20±√202−4(98)(−20)2(98)
color(white)("XXX")t = 0.56518sXXXt=0.56518s