# Homework Help: Factors that affect the trajectory of a projected mass.

1. Apr 6, 2006

### JMatch

This is my physics coursework task and although I have had only minor difficulties in actually doing the work, I thought I would post some of the things that I found to verify.

Basically, I began with saying that the initial speed (u), initial height (h), gravitational constant (g) and the angle of projection (the) all played a role in determining the horizontal displacement (d) of the projected mass.

I varied the initial speed (u) by constructing a ramp and changing the vertical height of the mass 'up' the ramp (H). Keeping h, g constant and $$\theta$$ = 0, enabled me to find the initial speed as $$v = \sqrt{2gH}$$ (using conservation of energy).

I then found the time it would take for the mass to hit the floor, $$t = \sqrt{(2h)/g}$$ and combining this with the value for v enabled me to find out the horizontal displacement (d) in terms of H and h. $$d = 2\sqrt{Hh}$$

That was the easy part. Deciding what factors made these theoretical results different from the experimental ones was a little harder.

Obviously air resistance will be a factor, as will the co-efficient of friction on the ramp. Those were the only two factors I could see that would make a difference.

I have a bit of a block when it comes to air resistance. I know I am wrong in thinking that air resistance is constant magnitude but varies in direction, however I am thinking it and it is annoying me.

Now I am forgetting the entire point of the task.. damn you PF!

(It should come to me soon, but any views so far?)

2. Apr 7, 2006

### andrevdh

If the mass was rolling down the ramp some of the potential energy would be converted to rotational kinetic energy.

3. Apr 7, 2006

### BobG

The magnitude of air resistance isn't constant. It increases when the velocity increases and decreases when the velocity decreases. Unless you have a wind, the air resistance always opposes the direction of motion - i.e. relative to the object's motion, the direction of air resistance is always constant.