A stone is thrown up from ground with a speed of 144 km/hr. The time gap at which the stone is at a height  of 60m from the ground g=10m/s2

by question, initial velocity=U=144 km/hr⇒U=144×518=40m/s2 acceleration due to gravity=a=−g=−10m/s2displacement=S=60mtime t=? we know,    S=Ut+12at2 ⇒60=40t+12−10t2⇒t2−8t+12=0 t=8±64−482⇒t=8±42 t=2ort=6 Hence the stone is at 60m after 2sec during upward motion and 6sec during down ward  motion.  The time gap between two instants is 6-2=4 second