A soap bubble is essentially a thin film of water surrounded by air. The colors you see in soap bubbles are produced by interference. What visible wavelengths of light are strongly reflected from a 390-nm-thick soap bubble? What color would such a soap bubble appear to be?

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A cylindrical beaker of height 0.100 m and negligible weight is filled to the brim with a fluid of density ρ = 890 kg/m^{3} . When the beaker is placed on a scale, its weight is measured to be 1.00 N .(Figure 1)

A ball of density ρb = 5000 kg/m^{3} and volume V = 60.0 cm^{3} is then submerged in the fluid so that some of the fluid spills over the side of the beaker. The ball is held in place by a stiff rod of negligible volume and weight. Throughout the problem, assume the acceleration due to gravity is g = 9.81 m/s^{2} .

Part A

What is the weight W_{b} of the ball?

Express your answer numerically in newtons.

Part B

What is the reading W_{2} of the scale when the ball is held in this submerged position? Assume that none of the water that spills over stays on the scale.

Calculate your answer from the quantities given in the problem and express it numerically in newtons.

Part C

What is the force Fr applied to the ball by the rod? Take upward forces to be positive (e.g., if the force on the ball is downward, your answer should be negative).

Express your answer numerically in newtons.

Part D

What weight W3 does the scale now show?

Express your answer numerically in newtons.

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**Part A **

What is the magnitude of the electric force on charge A in the figure?

F=______N

**Part B**

What is the direction of the electric force on charge A in the figure? Choose best answer.

- (a)to the left
- (b)to the right
- (c)the force is zero

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In (Figure 1), charge q_{2} experiences no net electric force. What is q_{1}?

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Two identical metal spheres A and B are connected by a plastic rod. Both are initially neutral. 4.0×1012 electrons are added to sphere A, then the connecting rod is removed. a)Afterward, what is the charge of A? b)Afterward, what is the charge of B?

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Several wires of varying thickness are all made of the same material and all have the same length. If the wires are arranged in order of decreasing thickness, what can be said about the ordering of their resistance?

- A. The wires will be arranged in order of increasing resistance.
- B. The wires will be arranged in order of decreasing resistance.
- C. The ordering of the resistances can not be determined because the resistivity is not given.
- D. The ordering of the resistances can not be determined because the length is not given.

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According to table 1, which of the following materials is the poorest electrical conductor?

- A. Nichrome
- B. Copper
- C. Aluminum
- D. Brass

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According to Table 1, which of the following materials is the best electrical conductor?

- Brass
- Copper
- Aluminum
- Nichrome

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The three masses shown in (Figure 1) are connected by massless, rigid rods. Assume that m_{1} = 180 g and m_{2} = 350 g.

What is the x-coordinate of the center of mass?

Express your answer with the appropriate units.

What is the y-coordinate of the center of mass?

Express your answer with the appropriate units.

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A frictionless pulley, which can be modeled as a 0.90kg solid cylinder with a 0.31m radius, has a rope going over it, as shown in the figure. The tensions in the rope are 12N and 10N. What is the angular acceleration of the pulley?

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A toy top with a spool of diameter 5.0cm has a moment of inertia of 3.0x10^-5kg x m^2 about its rotation axis. To get the top spinning, its string is pulled with a tension of .30 N. How long does it take for the top to complete the first five revolutions? The string is long enough that it is wrapped around the top more than five turns

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There are two reasonable approximations to consider for the pencil in this problem: a cylinder and a thin rod. However, in this problem, we will treat the pencil as a uniform thin rod of length 15.0 cm and mass 10.0 g.

The pencil rotates about an axis perpendicular to the plane of the figure. Which of the labeled points is the point that the axis of rotation passes through?

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There is a girl pushing on a large stone sphere. The sphere has a mass of 8200 kgand a radius of 90 cm and floats with nearly zero friction on a thin layer of pressurized water. Suppose that she pushes on the sphere tangent to its surface with a steady force of F = 30N and that the pressured water provides a frictionless support.

1) How long will it take her to rotate the sphere one time, starting from rest?

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A 250 g, 25-cm-diameter plastic disk is spun on an axle through its center by an electric motor.

What torque must the motor supply to take the disk from 0to 1600 rpm in 4.8 s?

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A regulation table tennis ball has a mass of 2.7g and is 40mm in diameter. What is its moment of inertia about an axis that passes through its center?

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