Monday, February 24, 2014

Practice Problems and review for Exam 1

Remember - Proper Preparation Prevents Poor Performance.

1. What are epicycles and why were they important?  What is retrograde motion and what is *actually* going on when mars seems to move backward?

2.  What contributions did Galileo make with his telescope? What got him into trouble?

3.  What is Copernicus' main contribution to science?

4. Know and understand the demonstrations with the "ball dropping and launching" cart.

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1. Know and understand Newton's laws of motion.

2.  A 10-kg object is pushed on by a 200-N force.  What will be the acceleration?

3.  What is the weight of a 100-kg man?

4.  Would the answer to 3 be different if he was on the moon?  How so?

5.  Consider yourself standing on a scale in an elevator.  The scale reads your weight.  Compared to being at rest, how would the scale reading change (if at all) if the elevator were:

A.  Moving with constant velocity upward
B.  moving with constant velocity downward
C.  Moving with constant acceleration upward
D.  Moving with constant acceleration downward
E.  If the cable snapped (yikes!) and the elevator were falling



6.  Give the name and publication on Newton's major book

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1. Describe each of Newton's 3 laws.

2. A 0.5 kg toy car is pushed with a 40 newton force. What is the car's acceleration?

3. Without calculating anything, what would be the effect (in problem 2) of increasing the mass of the car?

4. Give an example of Newton's 1st law in action.

5. Give an example of Newton's 3rd law in action.

6. Newton's "big book", what I claim is the most important non-religious book of all time is _____ and was published in _____.

7. What things are worth remembering about the so-called Scientific Revolution?

8.  Have a basic idea of historical chronology between these fellows:  Newton, Copernicus, Ptolemy, Galileo.  And roughly, why their contributions are important.

9.  What are epicycles and why are they important in the history of science?

10.  What is precession (wobbling) and why is it important in the history of science?

11.  Distinguish between weight and mass.

12.  What is the SI unit of force?  What is the English unit of force?

13.  How does weight depend on gravitational acceleration?

14.  Why do objects in freefall fall with the same acceleration?  Give one of the arguments that appeals to you.



Gravitation problems:

1.  Explain the meaning of "inverse square law".

2.  Discuss each of Kepler's 3 laws.

3.  At what point in its orbit is the Earth closest to the Sun?

4.  At what point in its orbit is the Earth moving fastest?

5.  What causes seasons?

6.  What is a semi-major axis of orbit (a)?

7.  What is an Astronomical Unit (AU)?

8.  Consider Jupiter.  It's orbit is 5 AU in size (roughly).  How long should it take Jupiter to orbit the Sun once?  Show how this calculation would be done.

9.  What is the period of Earth's orbit around the Sun?

10.  What is the size of Earth's orbit (in AU)?

11.  When you stand on the Earth's surface, you experience your "normal" Earth weight.  What would happen to your Earth weight if you were one Earth radius above the surface?  (That's twice as far from the center as simply standing on the surface.)

12.  What does gravitational force between 2 objects depend on?

(Answers below.)

General topics for exam 1.  Be sure to review all assigned homework, blog posts and your notes.

You are permitted to have a sheet of notes for this test.  I will NOT give equations.

pseudoscience
SI units (m, kg, s) - meanings, definitions
velocity
acceleration
related problems using the formulas
speed of light (c)
gravitational acceleration (g)
average vs. instantaneous velocity
freefall problems
Newton's 3 laws - applications and problems
Kepler's 3 laws - applications and problems
Newton's law of universal gravitation (inverse square law)
weight
the basics of flight

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1.  Explain the meaning of "inverse square law".

The force (of gravity, in this case) gets progressively weaker by the factor 1 over the distance squared.  Double the distance --> force is 1/4 as great as it was.  Triple the distance --> force is 1/9 the original.

2.  Discuss each of Kepler's 3 laws.

See notes.

3.  At what point in its orbit is the Earth closest to the Sun?

Perihelion, which is approximately January 3 each year.

4.  At what point in its orbit is the Earth moving fastest?

Same point as 3 above.

5.  What causes seasons?

Tilt of Earth's axis.

6.  What is a semi-major axis of orbit (a)?

Half the longest distance across the orbital path (ellipse).

7.  What is an Astronomical Unit (AU)?

Defined as the semi-major axis of Earth's orbit - roughly 93,000,000 miles - or  half the longest width across Earth's orbit.

8.  Consider Jupiter.  It's orbit is 5 AU in size (roughly).  How long should it take Jupiter to orbit the Sun once?  Show how this calculation would be done.

5^3 = T^2

So, T = the square root of 125.

9.  What is the period of Earth's orbit around the Sun?

1 year, or approximately 365.25 days.

10.  What is the size of Earth's orbit (in AU)?

Defined as 1 AU.

11.  When you stand on the Earth's surface, you experience your "normal" Earth weight.  What would happen to your Earth weight if you were one Earth radius above the surface?  (That's twice as far from the center as simply standing on the surface.)

1/4 your surface weight.

12.  What does gravitational force between 2 objects depend on?

mass of the objects; distance between; a universal (unchanging) constant (G)

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