# Hi all, please help me with a few physics problems.

1. Oct 17, 2007

### BigGirl58

1. The problem statement, all variables and given/known data

A dirt bike rider needs to complete a course that includes a "triple", a jump over three small hills that are speerated by a distance of 50 meters. The incline for the takeoff point is 37 degrees. How fast must the dirt bike rider travel to land 2.5 meters on the down side of the last hill?

2. Relevant equations

This is what I don't understand. I don't know what equation to use.

3. The attempt at a solution

None yet.

1. The problem statement, all variables and given/known data

A 75 kg paratrooper blacks out when experiencing downward forces in excess of 1000N. If he jumps out of a plane at 4000 meters and deploys his parachute at 2500 meters and the parachute causes an upward acceleration of 6 meters per second^2, will he black out? Why or why not?

2. Relevant equations

This is what I don't understand. I don't know what equation to use.

3. The attempt at a solution

None yet.

1. The problem statement, all variables and given/known data

A mobile TV camera is strung over an NFL stadium. The camera has a mass of 100 KG. There's a glitch in the rigging so the camera stalls and hangs down so that the angle between the 2 supporting cables is 45 degrees on the horizontal. What is the force (tension) on each cable?

2. Relevant equations

This is what I don't understand. I don't know what equation to use.

3. The attempt at a solution

None yet.

I've solved most of my problems. But these ones I don't understand how to approach. I'm not specifically looking for answers but just the proper way to attempt them. Answers are nice to check my eventual answers but I'll be attempting them myself either way. Thank you very much for reading!

Last edited: Oct 17, 2007
2. Oct 17, 2007

### Hootenanny

Staff Emeritus
Lets take question one first, do you know any kinematic equations?

3. Oct 17, 2007

### BigGirl58

Hmmm sounds familiar. That has to do with free-falling right?

4. Oct 17, 2007

### qspeechc

Equations of motion. Do you know them?

5. Oct 17, 2007

### BigGirl58

Somewhat I guess. Am I asking questiosn that are really basic? I'm very new to Physics is all. So many equations it's hard to figure out which goes where.

6. Oct 17, 2007

### Hootenanny

Staff Emeritus
Which kinematic equations [sometimes refered to as SUVAT equations] do you know?

7. Oct 17, 2007

### BigGirl58

I only have these ones in my notes:

Vfinal^2 = Vinitial^2 + 2 * a * d

Vfinal = Vinitial + a * t

8. Oct 17, 2007

### Hootenanny

Staff Emeritus
Not have any relating S, u, a and t?

9. Oct 17, 2007

### BigGirl58

Unfortunately, no. I'm a great notetaker and there's not an S or U anywhere here.

10. Oct 17, 2007

### Hootenanny

Staff Emeritus
Okay, nevermind, so the first step would be to split the take off velocity into vertical and horizontal components.

11. Oct 17, 2007

### BigGirl58

Hmm...so you mean how fast and how high?

12. Oct 17, 2007

### Hootenanny

Staff Emeritus
Nope, I mean splitting the velocity into a vertical velocity and horizontal velocity, we can write the vertical velocity thus;

$$v_y = v\sin\theta$$

Do you follow?

13. Oct 17, 2007

### BigGirl58

Ohhh okay yea, I follow. Sorry I'm blonde.

14. Oct 17, 2007

### Hootenanny

Staff Emeritus
So am I, although I'm not a women....

So, what would be the horizontal component of velocity?

15. Oct 17, 2007

### BigGirl58

would it be $$h_y = h\cos\theta$$

16. Oct 17, 2007

### Hootenanny

Staff Emeritus
Looks okay to me. Now, using the vertical velocity can you work out how long he would be in the air for?

17. Oct 17, 2007

### BigGirl58

Well, I know the Sin of 37 is .6 and the Cos is .8, but what is H and V?

18. Oct 17, 2007

### Hootenanny

Staff Emeritus
Lets stick you v's ok so;

$$v_x = v\cos\theta$$

where v is the magnitude of the velocity.

19. Oct 17, 2007

### BigGirl58

I'm sorry, I don't get it. Is V an actual number I'm missing? Thank you for being so patient.

20. Oct 17, 2007

### Hootenanny

Staff Emeritus
Yes, v is the number you're missing.

And no problem

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