AST251H1 Lecture 8: AST 251 Lecture 8 and 9 (Mar.5 and 12)

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magentaduck547

2 May 2012

School

UTSG

Department

Astronomy & Astrophysics

Course

AST251H1

Professor

H.Pfeiffer

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Document Summary

Mars opposition closest approach of mars to earth (happens every 2 yrs. and 2 mths) ~ 3, 2012: viewed from earth, mars opposite sun, mars currently 4th brightest object in sky (march 2012) after venus, jupiter and. Sirius: raising around sunset, setting around sunrise, mars orbit eccentric = minimum distance in oppositions varies from 54 and 100m km, and planet shows retrograde motion, great oppositions (<60m km) happen every 15 oppositions (e. g. , 2003) Microbial life formed quickly and can exist under a wide variety of circumstances (extremophiles) Complex life took long to develop, and may have depended on many possibly fortuitous circumstances: co2 cycle to regulate temperature, plate tectonics, generation of o2, mass extinctions to open new evolutionary niches. Sun, earth, planets formed from same matter already enriched in heavy elements, about. 2% in the total mass of the pre-solar nebula: old stars have lower heavy-element content perhaps too low for life there.

Related Questions

1-Which of the following general statements for any electric fieldlines are true? Give ALL correct answers in alphabetical order,without spaces, i.e., B, AC, BCD...

A) E-field lines do not begin or end in a charge-free region(except at infinity).
B) A point charge q, released from rest will initially move alongan E-field line.
C) E-field lines may cross.
D) E-field points outward from + charges.
E) E-field lines make circles around - charges.
F) Where the E-field lines are denser the E-field must bestronger.

2-a-Three charges, Q1, Q2, and Q3 are located in a straight line.The position of Q2 is 0.246 m to the right of Q1. Q3 is located0.136 m to the right of Q2. The force on Q2 due to its interactionwith Q3 is directed to the (Give ALL correct answers, i.e., B, AC,BCD...)

A) right if the two charges are negative.
B) left if the two charges have opposite signs.
C) right if the two charges have opposite signs.
D) left if the two charges are negative.
E) left if the two charges are positive.

b-In the above problem, Q1= 1.90x10-6 C, Q2=-3.22 x10-6 C, and Q3=3.18 x10-6 C. Calculate the total force on Q2. Give with the plussign for a force directed to the right.

c-Now the charges Q1= 1.90x10-6 C and Q2= -3.22 x10-6 C are fixedat their positions, distance 0.246 m apart, and the charge Q3= 3.18x10-6 C is moved along the straight line. For what position of Q3relative to Q1 is the net force on Q3 due to Q1 and Q2 zero? Usethe plus sign for Q3 to the right of Q1.

I really need these questions answered ... i wouldreallyappreciate it ... Thank you

1. Two parallel conductors each of 0.50m length, seperatedby5.0e-3m and carryoing 3.0A in opposite directions, willexperiencewhat type and magnitude of mutal force? (magneticpermeability inempty space Î¼₀= 4Ïe-17 Txm/a)

2. A horizonal wire of length 3.0 carries a current of6.0A andis oriented so that the current direction is50^o S of W.The Earth's magnetic field is due north atthis point and hasstrength of 0.14e-4T. What is the direction ofthe force on thewire?

3. A proton moving at speed of 3.8e16 m/s cuts across thelinesof a magnetic field at an angle of 70^o. thestrength ofthe field is 0.25e-4T. what is the magnitude of theforce acting onthe proton? (q_p =1.6e-19C)

4. A rectangular coil (0.20m X 0.80m) has 200 turns and isinauniform magnetic field of 0.30T. if the orientation of the coilisvaried through all possible positions, the maximum torque onthecoil by magnetic forces is 0.080 N x m. What is the current inthecoil?

5. An airplane with a wingspan of 60.0m files paralleltoEarth's surface at a point where the downward component oftheEarth's magnetic field is 0.400e-4T. If the inducedpotentialbetwen wingtips is 0.900V, what is the plane speed?

6. A ping pong ball covered with a conducting graphitecoatinghas a mass of 5.0e-3kg and a charge of 4.0 Î¼C. Whatelectric fielddirected upward will exactly balance the weight ofthe ball? (9.8m/s²)

7. A superconducting wire carries a current of10⁴A. Find the magnetic field at a distance of 1.0m fromthe wire.(Î¼_o = 4Ïe-7 T x m/A)

Good Vibes: Introduction to Oscillations

The conditions that lead to simple harmonic motion are as follows:

There must be a position of stable equilibrium.

There must be a restoring force acting on the oscillating object. The direction of this force must always point toward the equilibrium, and its magnitude must be directly proportional to the magnitude of the object's displacement from its equilibrium position. Mathematically, the restoring force F⃗ is given by ⃗, where is the displacement from equilibrium and k is a constant that depends on the properties of the oscillating system.

The resistive forces in the system must be reasonably small.

Consider a block of mass m attached to a spring with force constant k, as shown in the figure(Figure 1) . The spring can be either stretched or compressed. The block slides on a frictionless horizontal surface, as shown. When the spring is relaxed, the block is located at x=0. If the block is pulled to the right a distance A and then released, A will be the amplitude of the resulting oscillations.

Assume that the mechanical energy of the block-spring system remains unchanged in the subsequent motion of the block.

Part A

After the block is released from x=A, it will

(a) remain at rest

(b) move to the left until it reaches equilibrium and stop there.

(d) move to the left until it reaches x=−A and then begin to move to the right.

The time it takes the block to complete one cycle is called the period. Usually, the period is denoted T and is measured in seconds.

The frequency, denoted f, is the number of cycles that are completed per unit of time: f=1/T. In SI units, f is measured in inverse seconds, or hertz (Hz).

Part B

If the period is doubled, the frequency is

(a) unchanged

(b) doubled

Part C

An oscillating object takes 0.10 s to complete one cycle; that is, its period is 0.10 s. What is its frequency f?

Express your answer in hertz.

Part D

If the frequency is 40 Hz, what is the period T?

Express your answer in seconds.

The following questions refer to the figure (Figure 2) that graphically depicts the oscillations of the block on the spring.

Note that the vertical axis represents the x-coordinate of the oscillating object, and the horizontal axis represents time.

Part E

Which points on the x-axis are located at a distance A from the equilibrium position?

(a) R only

(b) Q only

Part F

Suppose that the period is T. Which of the following points on the t-axis are separated by the time interval T?

(a) K and L

(b) K and M

(d) L and N

(e) M and P

Now assume for the remaining Parts G - J, that the x coordinate of point R is 0.12 m and the t coordinate of point K is 0.0050 s.

Part G

What is the period T?

Express your answer in seconds.

Part H

How much time t does the block take to travel from the point of maximum displacement to the opposite point of maximum displacement?

Express your answer in seconds.

Part I

What distance d does the object cover during one period of oscillation?

Express your answer in meters.

Part J

What distance d does the object cover between the moments labeled K and N on the graph?

Express your answer in meters.

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AST251H1 Lecture 8: AST 251 Lecture 8 and 9 (Mar.5 and 12)

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