A rock is thrown straight up and reaches a height of 10 m. a) How long

1.	A rock is thrown straight up and reaches a height of 10 m. a) How long was the rock in the air? b) What is the initial velocity of the rock?
Answer» GIVEN : Maximum height attained = 10m To FIND : TIME taken by rock to reach there Initial velocity of the rock Solution : ❒ For a body thrown vertically upward, g is taken negative. Acceleration due to gravity has constant magnitude throughout the motion therefore equation of motion can be easily applied to solve this question. A] Calculation of Initial velocity : $\sf:\implies\:<klux>V</klux>^2-u^2=2gH$ At highest point v = 0 $\sf:\implies\:0^2-u^2=2(-10)(10)$ $\sf:\implies\:-u^2=-200$ $\sf:\implies\:u=\sqrt{200}$ $:\implies\:\underline{\boxed{\bf{\red{u=10\sqrt2\:m/s}}}}$ B] Calculation of time : $\sf:\implies\:v=u+gt$ $\sf:\implies\:0=10\sqrt2+(-10)t$ $\sf:\implies\:-10\sqrt2=-10t$ $:\implies\:\underline{\boxed{\bf{\pink{t=\sqrt2\:s}}}}$