A sound wave from a police siren has an intensity of 103.1 W/m2 at a certain point; a second sound wave from a nearby ambulance has an intensity level that is 14 dB greater than the police siren's sound wave at the same point. What is the intensity level of the sound wave due to the ambulance?

I'm teaching a conceptual introduction to physics for American 13-15 year old students this summer.

One of the main ideas I want to hit on is the relationship between energy conservation, equilibrium, and dissipative forces. (e.g. When a box sliding over the floor comes to rest, its kinetic energy mostly goes into heating the floor. We expect this because there there are many degrees of freedom in the floor, while the bulk motion of the box is at most six degrees of freedom.)

I'm looking for experiments and demonstrations of this effect. We can look at examples of turning mechanical work into heat (rub your hands together, hammer a nail, start a fire with friction), but this doesn't quite get across the idea of what thermal energy is. We might be able to observe Brownian motion, but since molecules are too small to see this has limited intuitive appeal for this age range.

Ideally, I'd like to find systems where you can actually see the "microscopic" degrees of freedom alongside the "macroscopic" degrees of freedom. This could be actual physics demonstrations, or artificial scenarios in the form of games the students play out on a field (perhaps following certain rules about the field's layout as individual decision makers, but inevitably creating a certain distribution of students in different "zones" on the field) or simulations on a computer.

All suggestions welcome, and if I implement it in the course next month, I'll report back on how it went.

(Mods, could you please mark this community wiki?)

1) The radioactive isotope 57Co has a half-life of 272 days.
(a) Find its decay constant.
(b) If your source has an activity of 2.00 mCi, how many radioactive nuclei does it contain?
(c) What is the activity of your source after one year?

A square uniform raft, 18.1m by 18.1m, of mass 6229kg, is used as a ferryboat. If three cars, each of mass 1176kg, occupy the NE, SE, and SW corners, determine the CM of the loaded ferryboat. Use east as the positive x-axis, north as the positive y-axis and the centre of the raft as the origin.

Y coordinate?

X Coordinate

A 2.15-kg object hangs in equilibrium at the end of a rope (taken as massless) while a wind pushes the object with a 18.5-N horizontal force. Find the magnitude of the tension in the rope, and the rope\'s angle from the vertical. The acceleration due to gravity is 9.81 m/s2.

A 6 kg sled is initially at rest on a horizontal road. The sled is pulled a distance of 2.8 m by a force of 36 N applied to the sled at an angle of 30o to the horizontal. Find the change in the kinetic energy of the sled.

Question 1

Which of the following are true statements about the electric field?

10 points   

Question 2

Which of the following are true statements about how magnetism is like electricity?

5 points   

Question 3

What is Faraday’s Law?

5 points   

Question 4

How does the magnetic field in the center of a solenoid change when the number of turns of the single wire is tripled?

shopper in a supermarket pushes a loaded cart with a horizontal force of 8 N. The cart has a mass of 26 kg.

(a) How far will it move in 2.0 s, starting from rest? (Ignore friction.)
1 m
(b) How far will it move in 2.0 s if the shopper places his 30 N child in the cart before he begins to push it?
2 m

Prove Carnot’s Theorem: No real heat engine operating between two energy reservoirs can be more efficient than a Carnot engine operating between the same two reservoirs.

A). Find the two locations where an object can be placed in front of a concave mirror with a radius of curvature of 36cm such that its image is twice its size. answer in cm

B). In the case when the object is placed closer to the mirror, state whether the image is real or virtual, upright or inverted.

C). In the case when the object is placed farther to the mirror, state whether the image is real or virtual, upright or inverted.

Two identical + 9.0 μC point charges are initially 3.5 cm from each other.

If they are released at the same instant from rest, how fast will each be moving when they are very far away from each other? Assume they have identical masses of 3.0 mg .

Express your answer using two significant figures.

You're driving down the highway late one night at 20m/s when a deer steps onto the road 54 m in front of you. Your reaction time before stepping on the brakes is 0.50s, and the maximum deceleration of your car is 10m/s2.

Part A How much distance is between you and the deer when you come to a stop? Express your answer to two significant figures and include the appropriate units.

s =

Part B What is the maximum speed you could have and still not hit the deer? Express your answer to two significant figures and include the appropriate units.

v=

1)If the coefficient of kinetic friction between tires and dry pavement is 0.800, what is the shortest distance in which an automobile can be stopped by locking the brakes when traveling at 26.0m/s ?

2)On wet pavement the coefficient of kinetic friction may be only 0.250. How fast should you drive on wet pavement in order to be able to stop in the same distance as in part A? (Note: Locking the brakes is not the safest way to stop.)

4. A uniformly charged dielectric solid sphere of radius a = 8 cm carries a total charge Q = 5 μC. Let the potential be zero an infinite distance away.

5. a) [26.6] What is the potential at the surface of the sphere?

6. b) [26.9] Sketch the graph of the potential due to the sphere from r = 0 to r = 20 cm.

7. c) [26.3] What work must be done to bring a 0.2 μC point charge from infinity to a point 16 cm from the center of the sphere?