for fun

http://autos.yahoo.com/blogs/motoramic/physicist-claims-victory-over-traffic-ticket-physics-paper-151808710.html

try - find currents, voltages.

Another may be forthcoming. Check back in a day or so.

HW

Related to yesterday's lab. Conceive of a way to determine internal resistance of a battery that we could test in class.Hooking the battery up to a multimeter directly doesn't count.

Circuits

1. Finish the problem from class, finding the currents everywhere in the circuit.

2. Let's consider a combination circuit. Two resistors (10 and 30 ohms) are in series. They are in series with a pair of resistors (60 and 120 ohms) in parallel with each other. Find the total resistance of the circuit and the individual currents and voltages for all resistors. Voltage is 20 V.

3. Consider three pairs of identical resistors (2, 4, 6, ohms). The pairs are in parallel, but these parallel pairs are in series with each other and with a 12-V battery. Solve for all currents and voltages.

4. If time allows, read about Kirchoff's rules for circuits. It's a different (and more useful) approach.

3 problem test

HW for next Tuesday

1. Solve the lab calculations:

Find experimental meter stick mass and compare to scale value.
Compare "left torque" to "right torque."

2. Review the rigid body CM problem for a cylinder.

3. Try the CM problem for a cube - prove that its CM is located 1/2 way up.

4. Try the CM problem for a right-circular cone. This one is tricky.

HW

1. Solve the general problem for the x-cm location, as measured from the left-most mass (m1). Check your text, to make sure you're right.

2. Use this to determine the location of the cm of the Earth/Moon system. Anything weird about this answer?

3. Look at the general expression for the cm of a rigid body. We'll delve into this in class.

4. Try these problem: ch.9 - 2, 4, if time do 3, 5, 6

HW

Finish elastic collision ramp problem from class

Also

1. Consider a typical force law for a sprng: F = k x

In this equation, x is displacement and k is a constant associated with how stiff the spring is (the opposite of how stretching it is)

Derive an expression for the work to stretch an "ideal" spring (one represented by the equation above). Note that this will also give you an expression for the energy stored in the stretched (or compressed) spring.


2. Try ch. 9 - 67, 69

hw for Wednesday

1. Try to estimate the area under the curve shown here - it is the impulse of the engine. Watch units and note that each block has an area of 0.3 N-s

http://www.321rockets.com/estes-b6-0-model-rocket-engines-1608

Do this calculation independently so that can compare values.

(The impulse is supposedly around 5 N-s.)

2. Each of the two groups has time data. I doubt that it will be meaningful, but use the width of your index card (in whatever orientation you had it) to estimate the velocity of your car. I suspect that this will be on the low end of correct values. Either measure the index card width directly or take data from a standard index card, folded as you had done in class.

3. See page 222 in your text for the standard solutions to the elastic collision problem discussed in class.

4. Finally, catch up on these problems:

chapter 9 - 54, 61, 68

HW for this Thursday

Lab is due at the beginning of class.

We will try to launch horizontal rocket cars, to compare impulse to change in momentum.

today

Today
Sorry that I'm out. If anyone is absent, let Tracey B know.

Today, work on the lab - due 2 classes from today.

It should have:

Abstract
Your technique or method
Calculations
Percent difference between the initial velocities found by the 2 methods
Conclusion

I'll post a few homework problems later. Use this time for the lab now.

Thanks.

hw from class today

Remember to revisit the igloo problem, seeking the alternate solution. 2/3 is indeed the answer.

Also, catch up on reading in the two energy chapters (7 and 8), focusing on the relationship between force and potential energy (derivative), discussed in 8-6.

Try also the Tarzan problem (8-25).

energy problems

1. Consider a brick dropped from a 15-m height. Find the following:

a. initial potential energy
b. kinetic energy immediately before hitting the ground
c. velocity immediately before impact with ground
d. velocity at a point half-way down

2. Consider a "loop the loop," in which a small mass is dropped from some height (H) and is free to slide frictionlessly until reaching a loop of radius r. (See picture on page 190, problem 8, for clarification).

What is the minimum height (H) so that the mass will "just make" the loop? Solve in terms of r (loop radius). [answer: H = 5r/2 (or 2.5r)

3. A large mass (m --> see, I told you it was large!) is moving at a speed v. It hits a friction-y surface (u) and slides to a halt. What is the distance that it will travel before completely stopping? (Solve for the distance in terms of relevant variables.)

Text problems worth a look, in this order (in case you are limited for time):

Chapter 8:

9 (watch units)
21
15
36* (tricky, but fun!)

Looking ahead

Flight data, take 1

HW

Hiya. Fun launching today, despite the ridiculous problems.

Try these problems, if you have time. Pick and choose, if time is short for you.

Chapter 6: 41, 43, 53, 81
Chapter 9: 29

Thank you.

Hw

Please read in chapter 9 - sections 3-7, 12

The momentum concept is an extension of Newton. If energy means nothing to you yet, don't worry about it.

Again, apologies for delay.

homework

Folks,

I've had a crisis to deal with so I was not able to post homework in a timely fashion. Also, I left my text at school. I'll post a couple of problems tomorrow morning. If you have time to try them, great. If not, I won't hold it against you.