A ball is thrown vertically upwards with a velocity v and an initial kinetic energy Ek. When half way to the top of its flight, it has a velocity and kinetic energy respectively of (A) v/square root 2, E/2 (B) v/4, E/2 or (C) v/2, E/square root 2 ?

Respuesta :

Answer:

Option A

[tex]\frac{V}{\sqrt{2} }[/tex] ,[tex]\frac{E}{2}[/tex]

Explanation:

When the ball its thrown up, at half way of its flight it means half of its vertical height which is [tex]\frac{h}{2}[/tex].  

potential energy = mgh

since it moved half way of height

P.E = [tex]\frac{mgh}{2}[/tex]

This means for the body to have gained half of its P.E, it will loose half of its kinetic energy.

Final kinetic energy([tex]E_{1}[/tex]) = E/2

kinetic energy = [tex]\frac{1}{2}mv^{2}[/tex]

let the final velocity at halfway flight be v1

[tex]E_{1}[/tex] = E/2

[tex]\frac{1}{2}mv_{1}^{2}[/tex] =[tex]\frac{\frac{1}{2}mv^{2}}{2}[/tex]

cross multiply we have

[tex]mv_{1}^{2}[/tex] =[tex]\frac{1}{2}mv^{2}[/tex]

cancel m from both sides

[tex]v_{1}^{2}[/tex] = [tex]\frac{1}{2}v^{2}[/tex]

take the square root of both sides,

[tex]v_{1} =\sqrt{\frac{v^{2} }{2} }[/tex]

[tex]v_{1} =\frac{v}{\sqrt{2} }[/tex]

Thus our final velocities will be E/2 and [tex] \frac{v}{\sqrt{2} }[/tex]