A ball projected at an angle of 45$^\circ$ with the horizontal crosses two points at equal heights separated by a distance at times 2 s and 8 s respectively. The horizontal distance between the two points is (Acceleration due to gravity = 10 ms$^{-2}$)
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For projectile motion, the sum of the two times at which the projectile is at the same height is equal to the total time of flight, $T = t_1+t_2$. This is a useful shortcut that bypasses the need to find the initial velocity and height.