Projectile Motion and Gravity: Calculating Height of a Projectile

[tibessiba]

Is this projectile motion??

Homework Statement

A projectile is shot straight up from the Earth's surface at a speed of 1.30×104 km/hr.

How high does it go?



Is this just a projectile motion problem? Or is it different because it has something to do with the theory of gravity? (because that is the section we are on in class).

 

[Feldoh]

Just a projectile motion problem.

 

[tibessiba]

Oh, ok...

Thanks

 

[Dick]

I think you mean 1.30*10^4km/hr, but I could be wrong. If so then it is fast enough that you can't take g=constant. So it's a gravity problem. It might be handy to know something about conservation of energy.

 

[tibessiba]

Oops.. Yes I do mean 1.30*10^4...

 

[Dick]

Ok, then you just need to know an expression for gravitational potential energy that is more general than mgh.

 

[Rylynn97]

I think it's a free-fall motion problem. You use the UAM (uniformly accelerated motion) formula d = (Vf^2 - Vi^2) / 2g, but make sure that g is negative since the projectile was shot upwards.

 

[Dick]

I think it's a free-fall motion problem. You use the UAM (uniformly accelerated motion) formula d = (Vf^2 - Vi^2) / 2g, but make sure that g is negative since the projectile was shot upwards.

Wrong, the projectile is moving at nearly orbital velocity. You can't take 'g' constant.

 

[rl.bhat]

Use conservation of energy principle.
KE = 1/2.mv^2
PE= GMm/(R + h). Substitute GM = gR^2. Find the value of h