# Homework Help: The mass of the pendulum bob was determined on an electronic scale and

1. Jul 27, 2012

### alicia113

The mass of the pendulum bob was determined on an electronic scale and its diamter was measured using calipers. The initial height was measured with a meter stick. At the lowest point of its swing, the pendulum bob broke a photogate light beam. The time interval that the light was interrupted was recorded on an electronic timer attached to the photogate.
Use the following data to complete a report.
MAss of pendulum bob = 240.3 g
Diameter of pendulum bob = 3.50 cm
Initial height of pendulum bob = 48.0 cm
Length of pendulum string = 2.14 m
Time interval of photogate light interruption = 11.8 ms

Your report should include the following:
(a) conclusion as to whether or not the pendulum demonstrated the law of conservation of energy
(b) calculations of the efficiency of the pendulum as a mechanical machine
(c) any statements of sources of error
(d) your suggestions for improving the design of the investigation.
Relevant equations[/b]

3. The attempt at a solution

Am I supposed to perform this experiement myself, becuase they are giving me all the measurments (therefore am I just doing an analysis) I am not quite sure how to go a outs this since they give me everything

To see if it obeys law of conservation Of energy I was going to see if the initial height matches the final hiring using 9.8m/s and my v ... Is that correct and how do I find efficnecy

2. Jul 27, 2012

### alicia113

Re: Pendlulum

Oh and I converted grams to kg and cm to m

3. Jul 27, 2012

### NoPoke

Re: Pendlulum

the experiment has been carried out for you (imagine that you watched it happening). You are then going to process the results.

I don't know what you mean by "final hiring using 9.8m/s"

What "v" are you referring to? You have yet to give a calculation for v, or to say what v is.

4. Jul 27, 2012

### alicia113

How do I calculate for v?

5. Jul 27, 2012

### alicia113

Re: Pendlulum

I know I use diameter and the 11.8 ms but I don't know the equation

6. Jul 27, 2012

### NoPoke

Re: Pendlulum

err you introduced v. I don't know what you mean by v.

By way of an extreme example I'm currently sitting still so my "v" I'd say was currently zero.

7. Jul 27, 2012

### alicia113

So if I use this equation

1/2mv^2+mgdeltah

It look like this.

0+0.3403 x 9.8m/s^2 x 0.48m?

Which equals 1.6 j as its initial spot at a...

8. Jul 27, 2012

### alicia113

Re: Pendlulum

Then for final height I did

0+ mgdeltah= 1.6J
(0.3403)(9.8m/s^2)deltah=1.6J

So delta h = 0.48 therefore it obeys the law?

9. Jul 27, 2012

### NoPoke

Re: Pendlulum

I'm stuck here. I don't know what you mean. I can't help with equations or verifying any answer until I know what steps you plan on using to answer the pendulum problem you have been set.

10. Jul 27, 2012

### alicia113

Re: Pendlulum

That's what I used above ?? I don't understand why they gave me so much info

11. Jul 27, 2012

### NoPoke

Re: Pendlulum

I've covered that...

12. Jul 27, 2012

### alicia113

And you are saying I need v.. So how to I get that? What equation do I use?

13. Jul 27, 2012

### NoPoke

Re: Pendlulum

You said you will use v in your opening post. You did not say what this v that you need is.

You need to say what v is before anyone can help you calculate it.

14. Jul 27, 2012

### alicia113

Re: Pendlulum

So v is 0 for the first hieght. The starting hieght at 0.48m r 48cm .. Because it is not moving.

I need to know what v is for the final so I can determine te hieght. So how do I find v when I have calculate the J for E mechancal. As posted above in previouse post

15. Jul 27, 2012

### NoPoke

Re: Pendlulum

You still are not saying what v is. For example every pendulum I've ever seen eventually stops so my final value is going to be zero. But that does not help you because I haven't said what I mean by v. On one pendulum clock I saw the escapement broke and the pendulum was thrown across the room. Numbers alone have no meaning.

Describe what you mean by v in words. Make it very clear so there can be no misunderstanding.

16. Jul 27, 2012

### alicia113

Re: Pendlulum

Ok v is speed sorry

17. Jul 27, 2012

### NoPoke

Re: Pendlulum

speed of what?

18. Jul 27, 2012

### alicia113

Re: Pendlulum

Of the pendulum when it hits its final hieght ...

19. Jul 27, 2012

### NoPoke

Re: Pendlulum

How will knowing that value help you? [You need a plan for how you are going to answer the question in your opening post]

20. Jul 27, 2012

### alicia113

Re: Pendlulum

Yes so my initial speed v is 0m/s as when it starts at intial hieght at 0.48m it is not moving. I need to find out the speed when it moves to the other side and need that hieght I determine if it obeys the law or not.