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Physics 121 Interval Test 3: Conceptual and Short Answer Questions, Study notes of Physics

New Mexico Institute of Mining & Technology (NMT)Physics

The third interval test for the physics 121 course, focusing on conceptual and short answer questions. Topics include gravitational forces, torque, angular velocity, and circular motion. Students are required to answer questions related to the properties of objects on spherical planets, the units of newton's universal gravitational constant, and the relationship between angular velocity and time. The document also includes problems on the calculation of torque for various diagrams and the motion of a comet in an elliptical orbit.

Typology: Study notes

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Uploaded on 08/08/2009

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YOUR NAME – _____________________________________

PHYSICS 121 – Interval Test #3 of 3

General Instructions: All answers should include (SI) units. All answers should have 3

significant figures. If you need “g” on Earth, you may use 10.0 m/s*s to save time.

Constants:

11

6.6710

G

−

=× (SI units)

Material Constants: Young’s modulus for steel cable.

112

2.010/

Steel

YNm

=×

Young’s modulus for Nylon rope.

92

1.010/

Nylon

YNm

=×

Astronomical Constants: Masses: 24

5.9710

Earth

Mkg

=× , 23

6.4210

Mars

Mkg

=×

Radii: 6380

Earth

Rkm

= 3397

Mars

Rkm

= 6.0

Deimos

Rkm

=

Periods: 7

13.1510

years

=×

Distance between Earth and Sun: 11

1.5010

EarthSun

Rm

−=×

Part I – CONCEPTUAL AND SHORT ANSWER (Approx 4 points each)

Only the correct answer is required for full credit (unless specified), though of course partial

credit can only be given if some work is shown.

1) An object is lifted from the surface of a spherical planet to an altitude equal to the radius

of the planet. As a result, which of the following changes in the properties of the object

take place?

a. Mass increases; weight decreases

b. Mass increases; weight remains the same

c. Mass remains the same; weight decreases

d. Mass decreases; weight decreases

e. Mass increases; weight increases

f. Mass remains the same; weight remains the same

2) The value of Newton’s universal gravitational constant, G, is quoted in “SI” units (the

ones we have used for the entire course) at the top of the page. What ARE the correct

units for G? (in terms of seconds, newtons, kg, m, joules, watts, radians/sec etc.)

3) What angle in degrees is subtended by an arc of 1.49 meters on the circumference of a

circle of radius 2.51 m? (Give an answer in radians and another in degrees).

4) The angle

θ

through which a bike wheel turns is given by

23

()

tabtct

θ

=+−

,

where a, b and c are positive constants such that

θ

is in radians for t in seconds.

At what time is the angular velocity of the wheel instantaneously not changing?

(Express answer in terms of a, b, c etc.)

5) Each of the bars shown can rotate freely

in the horizontal plane about its left end.

For which diagrams is the net torque

equal to zero? (Circle any that apply).

Partial preview of the text

Download Physics 121 Interval Test 3: Conceptual and Short Answer Questions and more Study notes Physics in PDF only on Docsity!

YOUR NAME – _____________________________________

PHYSICS 121 – Interval Test #3 of 3 General Instructions: All answers should include (SI) units. All answers should have 3 significant figures. If you need “g” on Earth, you may use 10.0 m/s*s to save time.

Constants: G = 6.67 × 10 −^11 (SI units)

Material Constants: Young’s modulus for steel cable. YSteel = 2.0 × 1011 N / m^2

Young’s modulus for Nylon rope. YNylon = 1.0 × 109 N / m^2

Astronomical Constants: Masses: M Earth = 5.97 × 10 24 kg , M Mars = 6.42 × 1023 kg

Radii: REarth = 6380 km RMars = 3397 km RDeimos =6.0 km

Periods: 1 year = 3.15 × 107 s

Distance between Earth and Sun: REarth (^) − Sun = 1.50 × 1011 m

Part I – CONCEPTUAL AND SHORT ANSWER (Approx 4 points each) Only the correct answer is required for full credit (unless specified), though of course partial credit can only be given if some work is shown.

An object is lifted from the surface of a spherical planet to an altitude equal to the radius of the planet. As a result, which of the following changes in the properties of the object take place? a. Mass increases; weight decreases b. Mass increases; weight remains the same c. Mass remains the same; weight decreases d. Mass decreases; weight decreases e. Mass increases; weight increases f. Mass remains the same; weight remains the same
The value of Newton’s universal gravitational constant, G, is quoted in “SI” units (the ones we have used for the entire course) at the top of the page. What ARE the correct units for G? (in terms of seconds, newtons, kg, m, joules, watts, radians/sec etc.)
What angle in degrees is subtended by an arc of 1.49 meters on the circumference of a circle of radius 2.51 m? (Give an answer in radians and another in degrees).
The angle (^) θ through which a bike wheel turns is given by θ ( ) t = a + bt^2 − ct^3 , where a, b and c are positive constants such that (^) θ is in radians for t in seconds. At what time is the angular velocity of the wheel instantaneously not changing? (Express answer in terms of a, b, c etc.)
Each of the bars shown can rotate freely in the horizontal plane about its left end. For which diagrams is the net torque equal to zero? (Circle any that apply).

A comet of mass m=10,000 kg in an elliptical orbit around the sun has a velocity of magnitude vPerihelion =100 m/s and a closest approach distance RPerihelion = 5.0 × 1010 m. When it reaches aphelion, the velocity has slowed to v (^) Ahelion = 20 m / s. What is the furthest distance of the comet from the sun? ( RAphelion = ?).
Justify in one sentence, what physical principle(s) allowed you to do the calculation in the previous problem?

A (giant) ladybug clings to a large merry-go-round as shown. (“Clings’ … that means it doesn’t walk around at all on the merry-go-round). The merry-go-round is 3 meters in radius, and the ladybug is at the edge. The x, y, z axes shown in the picture are fixed to the ground, so that they DO NOT rotate with the merry-go-round.

For the next three problems, assume that the merry go round was started up by an active child until it attained a constant rotation rate of 120 rpm.

What is the bug’s linear velocity v v in direction and magnitude when the bug is in the position indicated?
What is the merry-go-round’s angular velocity ω v in direction and magnitude when the bug is in the position indicated in the Figure. (use ˆ ˆ i j, k ,^ ˆ to indicate directions)

Part II – LONG ANSWER Use the ultra-abbreviated “ISEE” method.

USE UP AT LEAST A HALF PAGE OF PAPER FOR EACH PROBLEM! “I” – Sketch (where needed … not all problems need sketches), define variables and target variables where not obvious. “S” – List key equations and specialize to problem at hand. “E1” – Solve algebraicly for target variables. Plug in numbers and arrive at a numerical answer where possible. Your answer MUST include proper units. “E2” – There is no, E2.