Projectile Motion and maximum height

[wowdusk]

Homework Statement

A projectile is launched with a speed of 40 m/s at an angle of 60 degrees above the horizontal. Use conservation of energy to find the maximum height reached by the projectile during its flight.

Homework Equations

KEi+PEi=KEf+PEf

The Attempt at a Solution

i am not sure where vf would come from. Would it be just Vi*cos(60)?
I am not sure why that makes sense.
Does Vix=Vf?...and why?

 

[LowlyPion]

Homework Statement

A projectile is launched with a speed of 40 m/s at an angle of 60 degrees above the horizontal. Use conservation of energy to find the maximum height reached by the projectile during its flight.

Homework Equations

KEi+PEi=KEf+PEf

The Attempt at a Solution

i am not sure where vf would come from. Would it be just Vi*cos(60)?
I am not sure why that makes sense.
Does Vix=Vf?...and why?

Assume your potential energy is 0 when you launch and your kinetic energy in the y direction is what? 1/2*m*Viy²?

And at the height it has no vertical kinetic energy and the potential energy is what?

What is the vertical component of V? (Hint: it's not Vi*cos(60))

 

[wowdusk]

why do i need the vertical component of Vi

I don't know how to find the V at the heighest point...

At the heighest point is the V in vertical direction 0 anyway?

 

[wowdusk]

I think i solved this out...i got 61m?

 

[LowlyPion]

why do i need the vertical component of Vi

I don't know how to find the V at the heighest point...

At the heighest point is the V in vertical direction 0 anyway?

Yes your final V is 0.

But your initial V is the vertical component of V, as that is the component of V that is affected by gravity ... you know, where that potential energy is building.

 

[wowdusk]

Thank you...can you check if my answer is right?