# Projectile Questions

1. Dec 6, 2015

### TheRandomCrab

• Member warned to show an attempt at solution, complete template.
1. The problem statement, all variables and given/known data
Questions: 1. What can be said about the energies of the projectiles launched at different angles? Explain.

2. Will the projectiles launched at different angles hit the ground with the same force or with different forces?
Explain.

2. Relevant equations

3. The attempt at a solution

2. Dec 6, 2015

### Student100

I think you should explain, you're missing your attempt at the solution. What have you done so far? What are your thoughts on the matter?

3. Dec 6, 2015

### TheRandomCrab

The energies decrease as the angle gets bigger and the projectiles launched at different angles hit the ground with with the same force, its an introduction to physics just a little confused. But thats what I think.

4. Dec 6, 2015

### Student100

Why would the energies decrease as the angle gets larger? Assuming a uniform launch, what is final and initial energies of the projectile launched at various angles? What about the conservation of energy?

5. Dec 6, 2015

### TheRandomCrab

I keep reading that the initial kinetic energy is sporadic or it goes up and down depending on the angle.

6. Dec 6, 2015

### Student100

Come again?

How would the angle change the amount of energy of the projectile? Think about it for a second.

Think about a spring loaded gun, does the energy stored in the spring have any knowledge of the angle it's pointing in?

7. Dec 6, 2015

### TheRandomCrab

I know thats what Im reading I thought the same.

8. Dec 6, 2015

### azizlwl

Energy is scalar.

9. Dec 6, 2015

### haruspex

Can you provide an exact quote for that, specifying the context?
There is a subtlety here. The max KE during the upward flight will be when the spring reaches its relaxed length. If pointing up at some angle, it will already have raised the object against gravity. The steeper the angle, the more the work that was spent on that, so the less available for KE.
To avoid such details, sometimes the question specifies 'ground level' as the original height of the projectile. Thus, all of the original spring energy is available as KE when it hits the ground.

10. Dec 6, 2015

### TheRandomCrab

So do they hit the ground with the same force

11. Dec 6, 2015

### haruspex

"Force" would not be the right term, despite popular usage. They would land at the same speed, so the same KE and the same magnitude of momentum. The force on the projectile from the ground depends on the time and distance that the projectile takes to stop. And, being a vector, it also depends on the angle of impact.

12. Dec 6, 2015

### TheRandomCrab

I need to write two paragraphs on these 2 questions anything more?

13. Dec 6, 2015

### haruspex

Are you sure you have provided the entire question as set to you, word for word?
The reference to "the projectiles" suggests some missing preamble.

14. Dec 6, 2015

### TheRandomCrab

Yep entire questions

15. Dec 6, 2015

### Student100

You still haven't answered number 1 (I think), the question states energy, not just KE. So is there any difference dependent on the angle?

16. Dec 6, 2015

### TheRandomCrab

I don't know uhhhhh

17. Dec 6, 2015

### Student100

Lets make some assumptions: We have an isolated system, the projectile is launched from ground level, none of the initial energy from the launch is converted into internal energy, it doesn't rotate, we ignore the collision with the ground, and there are no external forces acting on the projectile/launcher.

Dependent on the angle of launch, some of the initial KE is converted into a form of potential energy: mgh. The greater the angle, the more KE is getting converted into gravitational potential energy on the arc upwards, does the total energy of the system change in this case?

Imagine it is just pointed up at 90 degrees, so that at the peak of the flight when the KE is 0, all the energy is potential. When it returns to ground level and gravitational potential energy is 0, KE is maxed. What can you say about the energy dependent on angle of launch? Then look at an angle of 0 so that the projectile rolls across the ground, without external forces acting on the projectile, all the energy in this case is kinetic. Is this initial and final energy a greater value than the energy of the 90 degree launch?

I think something along these lines is what the questions trying to get you to think about, maybe I'm wrong.

18. Dec 6, 2015

### TheRandomCrab

There but not quite. I can base this off of a data sheet with distance and angles time etc.. and such

19. Dec 6, 2015

### Student100

Can you elaborate on what you mean?

20. Dec 6, 2015

### TheRandomCrab

Its like a lab based on projectile motion