The figure shows an initially stationary block of mass m on a floor. A force of magnitude 0.500mg is then applied at upward angle θ = 20°. What is the magnitude of the acceleration of the block across the floor if (a) μ_s = 0.630 and μ_k = 0.530 and (b) μ_s = 0.430 and μ_k = 0.320?

The next two questions refer to the following physical situation:

Two blocks (masses m₁ = 30 kg and m₂ = 7 kg) sit atop one another as shown below. The coefficient of static friction between the blocks is μ_s= 0.32.  There is no friction between the lower block and the surface on which it rests. A constant external force F is applied to the lower block.

What is F_max, the maximum magnitude of this force such that the upper block does not slide with respect to the lower block?

If there is kinetic friction between the lower block and the surface, the magnitude of the maximum possible force F_max that can be exerted on the lower block before the upper block starts sliding with respect to the lower block...

A precocious child wants to determine the moment of inertia, I_o, of the local merry-go-round. The child measures the radius of the merry-go-round (R = 2 m), then weighs herself (m = 25 kg), then notices that when she moves from the center of the merry-go-round to the rim, the rotational velocity of the merry-go-round changes from 0.3 rev/sec to 0.2 rev/sec. If the child treats herself as a point mass, what moment of inertia does she estimate for the merry-go-round?

As the child moves from the center of the merry-go-round to the rim, the kinetic energy of the child plus the merry-go-round...

1. If a disk and a ring both have the same mass and radius, which one has the greater moment of inertia? Why is this so?
2. A figure skater doing pirouettes spins faster when she tucks her arms close to her chest and spins slower when she spreads out her arms. Explain this in terms of moment of inertia and Newton’s Second Law for rotational motion.

A cylindrical proportional tube has an anode wire radius of 0.003 cm and a cathode radius of 2.0 cm. It is operated with an applied voltage of 2000 V. If a minimum electric field of 1.0 MV/m is required to initiate gas multiplication, what fraction of the internal volume of the tube corresponds to the multiplication region?

A 0.92 kg mass is attached to a light spring with a force constant of 30.9 N/m and set into oscillation on a horizontal friction-less surface. If the spring is stretched 5.0 cm and released from rest, determine the following.

(a) maximum speed of the oscillating mass? in m/s ?

(b) speed of the oscillating mass when the spring is compressed 1.5 cm? in m/s ?

(c) speed of the oscillating mass as it passes the point 1.5 cm from the equilibrium position? in m/s ?

(d) value of x at which the speed of the oscillating mass is equal to one-half the maximum value? in m?

An apple falls from a tree and feels no air resistance. As it is falling, which of the following statement is correct?

After a trip to the store a 70.0-kg person is carrying heavy bags perpendicular to the direction of motion. How much work is being done by the person on the bags? Use the definition of work to show your result.

b) He takes a rest on a bench and leaves his bags on the ground. Sketch a free-body diagram for each of the three objects shown in the Figure.

c) Once he gets back to his apartment building he takes an elevator up. What acceleration of the elevator is necessary for his weight to increase by 10.0%?

Two converging lenses

(f₁ = 9.40 cm

and

f₂ = 5.50 cm)

are separated by 17.9 cm. The lens on the left has the longer focal length. An object stands 12.4 cm to the left of the left-hand lens in the combination. Locate the final image relative to the lens on the right. Obtain the overall magnification. Is the final image real or virtual? With respect to the original object, is the final image upright or inverted and is it larger or smaller?

(a) Locate the final image relative to the lens on the right.
cm  ---Select--- to the right of the right-hand lens to the left of the right-hand lens

(b) Obtain the overall magnification.


(c) Is the final image real or virtual?

realvirtual    

(d) Is the final image upright or inverted?

uprightinverted    

(e) Is it larger or smaller?

largersmaller   

(about solid state physics, optical communication)
The main principle of optical communication is the concept of total reflection. I wonder if the total reflection is based on particle property of light, or wave property of it.

The total reflection is the concept of refraction and reflection. I know that refraction and reflection of light are all properties that correspond to the particle and wave of light.(I mean, Particle property of light can explain refraction and reflection, and Wave property of light too.)
So.. Is it right if total reflection is using(based on) both particle and wave properties of light???

(c) Discuss the Minkowski spacetime diagrams. Show the world lines for a particle at rest and a photon on such a diagram. Explain the concept of light cones and draw it on your diagram.

a tire is filled with air at 14 ∘c to a gauge pressure of 230 kpa

If the tire reaches a temperature of 35 ∘C∘C, what fraction of the original air must be removed if the original pressure of 230 kPakPa is to be maintained?

A mass of 3 kg of water at 50oC has been heated to vapour at a temperature of 125oC in an oven. The specific heat capacities for water in the form of liquid (Cw), solid (Cice) and gas (Cv) are 4.187 kJ.kg-1.K-1, 2.108 kJ.kg-1.K-1, and 1.996 kJ.kg-1.K-1, respectively. Also, latent heats of fusion and vaporization are given as 3.33 x 105 J.kg-1 and 2.22 x 103 J.kg-1, respectively. NB: Number your answers correctly!

(a) What would be the entropy of water in the form of liquid, SL? (5)

(b) Calculate the entropy of the system when it changes its state/phase to vapour, Sv. (3)

(c) Compute the total entropy, STotal, of water between 50 oC and 125 oC. (5)

1.For an angle of zero between the magnetic field and the vector normal to the plane of the coil: (a) What happens to the light bulb as it enters the magnetic field region? Explain. (b) What happens to the light bulb as it moves while it is completely inside the magnetic field? Explain. (c) What happens to the light bulb as it exits the magnetic field region? NOTE: Use Faraday’s Law to explain.

2.For an angle of zero between the magnetic field and the vector normal to the plane of the coil: What happens to the light bulb when the you flip the direction of the magnetic field? Explain using Faraday’s Law.

3.For an angle of zero between the magnetic field and the vector normal to the plane of the coil: What happens to the light bulb when the magnitude of the magnetic field varies? Explain using Faraday’s Law

4.For an angle of zero between the magnetic field and the vector normal to the plane of the coil: What happens to the light bulb when the coil moves vertically? Explain using Faraday’s Law

fred places two circular loops of conducting wire, one large (radius R) and one small (radius r),
on a horizontal table such that they are centred at the same point. He arranges the larger loop
to carry a constant current I clockwise (when viewed from above). In order to induce a current
in the smaller loop, fred then lifts the smaller loop vertically upwards at a constant speed v,
without changing its orientation.
1 - Explain why fred is correct to expect an induced current in the smaller loop, and determine which way this current will flow.
2 - Show that the emf induced in the small loop is approximately
E = (U_03IR^2v/2z^4)*PIr^2
where z is the height above the table. You may use the result that the magnetic field
along the z-axis produced by the large loop is B = µ_0IR^2/2z^3. Make sure to explain,
with the aid of a diagram, the simplifying assumptions you need to make.
3 - Meanwhile sam, who is also in the room, happens to be levitating upwards at the same
velocity as the small loop. Thus the small loop is stationary in her frame. Explain,
from sam’s point of view, why she should also expect to see an induced emf in the small
loop. Your explanation should comment on the differences between fred’s and sam’s
description of the cause of the emf and explain how it is that they can both be correct.