# Answer on Mechanics | Relativity Question for danica

Question #1240

Sam tosses a ball horizontally off a footbridge at 3.1 m/s. How much time passes after he releases it until its speed doubles?

Expert's answer

The horizontal projection is constant while the vertical is changing according to the equation

V

(we chose the downward direction as positive).

V

V

V

V = √(V

V

(3.1

t =√(3.1

V

_{y}=V_{0y}+gt(we chose the downward direction as positive).

V

_{x}= 3.1 m/sV

_{0y}= 0;V

_{0}= 3.1 m/sV = √(V

_{x}^{2}+ V_{y}^{2}) = √(3.1^{2}+100t^{2})V

^{2}/V_{0}^{2}= 4(3.1

^{2}+100t^{2})/ 3.1^{2}= 4t =√(3.1

^{2}*3 / 100) = 0.54 sNeed a fast expert's response?

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