Exploring the Fundamentals of Motion and Forces: A Brief Overview

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In summary, the conversation discussed various topics in physics, including units of measurement, expressions, velocity, acceleration, forces, work, power, momentum, and angular speed. It also covered examples and calculations related to these concepts, such as converting units, finding net displacement, and determining the radius of curvature for creating weightlessness in an aircraft.
  • #1
wakejosh
102
0
I don't expect anyone to really go through all this and double check everything, but If anyone notices anything that is wrong maybe brushing over it please tell me. Thanks


1. On planet Z, the standard unit of length is the foose. Ann the
Astronaut is 5.90 feet tall on earth. She lands on planet Z and is measure to be 88 foosi (plural of foose) tall. Her crew member Rachael is 94 foosi tall. How tall is Rachael in Earth measurements?

e. 6.3


2. Note the expression: y = A/x2. Which statement is most consistent
with this expression?

a. y is less than x

3. The speed of a boat is often given in knots. If a speed of 5 knots were expressed in the SI system of units, the units would be:

c. m/s

4. A ball is pushed with an initial velocity of 4.0 m/s. The ball rolls down a hill with a constant acceleration of 1.6 m/s2 . The ball reaches the bottom of the hill in 6.0 s. What is the ball's velocity at the bottom of the hill?

c. 14 m/s

5. A European sports car dealer claims that his car will accelerate at a constant rate from rest to a speed of 100 km/hr (28 m/s) in 8.00 s. What is the speed after the first 5.00 s of acceleration?

d. 17.4 m/s

6. An object is dropped from a height and falls for several seconds. Which of the following statements can be true at some time during the fall.

Its velocity is more than its acceleration.
Its velocity is less than its acceleration.
Its velocity is the same as its acceleration.

d. All of the above can be true. (But not at the same exact time)

7. Which of the following is an example of a vector quantity?

c. displacement

8. Arvin the Ant is on the picnic table. He travels 30 cm eastward,
then 25 cm northward, and finally 15 cm westward. What is the magnitude of Arvin's net displacement?

d. 29 cm

9. A river flows due east at 3.0 m/s. A boat crosses the river which is 300 m wide, by maintaining a constant velocity of 10 m/s due north relative to the water. If no correction is made for the current, how far downstream does the boat move by the time it reaches the far shore?

d. 90 m


10. A 2.0 kg bowling ball experiences a net force of 4.0 N. What will
be its acceleration?

b. 2.0 m/s2


11. If we know that an object is moving at a constant velocity, we may
assume:

a. The net force acting on the object is zero.


12. As a car skids with its wheels locked trying to stop on a road
covered with ice and snow, the force of friction between the icy road and the tires will usually be: (Please note that "normal" and "perpendicular" have the same meaning)

c. less than the normal force of the road times the coefficient of
kinetic friction

13. As an object is lowered into a deep hole in the surface of the
earth. How does the potential energy of the object at the bottom of the hole compare with its potential energy at the top of the hole.

b. The potential energy at the bottom is less.


14. A 60 kg woman runs up a flight of stairs having a rise of 4.0 m in
a time of 6.0 s. What average power did she supply?

a. 400 W

15. A horizontal force of 100 N is applied to move a 45 kg cart across
a 9.0 m level surface. What amount of work is done by the 100 N force?

d. 900 J


16. A 50 kg swimmer dives horizontally off a 75 kg rowboat. If the
speed of the rowboat immediately after the swimmer dives off is 1.0 m/s, what speed did the diver leave the rowboat?

b. 1.5 m/s

17. The impulse experienced by an object is equivalent to its change
in:

d. momentum

18. In a system with two moving objects, when a collision occurs
between the two objects, what is conserved?

b. the total momentum is always conserved


19. A grindstone spinning at the rate of 8.3 rev/s has what
approximate angular speed?

d. 52 rad/s

20. A ventilation fan has blades 0.25 m long rotating at 2 rad/s. What is the centripetal acceleration of a point on the outer tip of a blade?

a. 1.0 m/s2

21. An airplane is a wide sweeping "outside" loop can create zero "g"
(weightlessness) inside the aircraft cabin. What must be the radius of curvature of the flight path for an aircraft moving at 70 m/s to create a condition of "weightlessness" inside the aircraft?


c. 500 m

22. A ventilation fan with a moment of inertia of 0.034 kg-m2 has a
net torque of 0.11 N-m applied to it. What angular acceleration does it experience?

c. 3.2 rad/s2


23 A bowling ball has a mass of 7.0 kg and a radius of 0.1 m. If it
rolls down the lane without slipping at a linear speed of 4.0 m/s, what is its angular velocity?

d. 40.0 rad/s


24. An ice skater spins at 2.5 rev/s when his arms are extended. He
draws his arms in and spins at 6 rev/s. By what factor does his moment of inertia change in the process?

c. 0.42
 
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  • #2
2 - I don't see why that statement has to be true (whats the other options)?

5 - I Realise that it is multiple choice, I take it there's no [itex]17.5ms^{-1}[/itex]

6 - Don't like this question, but I think you answered it right; saying velocity is the same as acceleration, is like saying an apple is the same as a banana! :biggrin:

12 - Why is it less?

21 - Agree unless there was a 490m option.

24 - Disagree! The mans rotational energy stays constant i.e:
[tex]\frac{1}{2} I_1 \omega_1^2 = \frac{1}{2} I_2 \omega_2^2[/tex]

So the factor it changes by is:
[tex]\frac{\omega_1^2}{\omega_2^2}[/tex]

not [tex]\frac{\omega_1}{\omega_2}[/tex]

Apart from that, looks good! :smile:

Regards,
Sam
 
  • #3
I would have another look at 2, 4, 5, 6, 12, and 14

In 2, if x2 means x2 what about the case when x<1?

In 4, the answer would be 14 with an accuracy of two signficant figures. The problem is that if the initial speed was 0, the speed after 6 seconds would be 9.6 m/sec. If you add 4.0 m/sec, you get 13.6 m/sec not 14.

5 should be 17.5

6, you cannot compare velocity and acceleration like that.

12 - by definition the friction force is equal to [itex]\mu_kN[/itex]

14. the answer is right if you are using g = 10 m/sec^2 but it should be 390 if 9.8 m/sec^2 is used.

the others look right.

AM
 
  • #4
BerryBoy said:
2 - I don't see why that statement has to be true (whats the other options)?
here is the full question:

2. Note the expression: y = A/x2. Which statement is most consistent
with this expression?

a. y is less than x b. if x is halved, y is multiplied by 4
c. y is greater than x d. if x is doubled, y is multiplied by a factor of 2
e. y is equal to x
 
  • #5
here is the full number 6:

6. An object is dropped from a height and falls for several seconds.
Which of the following
statements can be true at some time during the fall.

a. Its velocity is more than its acceleration.
b. Its velocity is less than its acceleration.
c. Its velocity is the same as its acceleration.
d. All of the above can be true. (But not at the same exact time)
e. None of the above can be true for a falling object
 
  • #6
wakejosh said:
here is the full question:

2. Note the expression: y = A/x2. Which statement is most consistent
with this expression?

a. y is less than x b. if x is halved, y is multiplied by 4
c. y is greater than x d. if x is doubled, y is multiplied by a factor of 2
e. y is equal to x
As Andrew pointed out, (a) is not right. It's (b) or (d); look at both, and calculate which it must be.
 
  • #7
here is 12:

12. As a car skids with its wheels locked trying to stop on a road
covered with ice and snow, the force of friction between the icy road and the tires will usually be: (Please note that "normal" and "perpendicular" have the same meaning)

a. greater than the normal force of the road times the coefficient
of static friction
b. equal to the normal force of the road times the coefficient of
static friction
c. less than the normal force of the road times the coefficient of
kinetic friction
d. greater than the normal force of the road times the coefficient
of kinetic friction
e. equal to the normal force of the road times the coefficient of
kinetic friction.


I know its Kinetic friction, but i wasnt sure completely on the comparison to the normal force of the road. I thought since the road was icy it should be less than normal, Is this wrong?
 
  • #8
geoffjb said:
As Andrew pointed out, (a) is not right. It's (b) or (d); look at both, and calculate which it must be.
well i know it can't be B so it must be D, and that makes sense when i run a few numbers through it.
 
  • #9
wakejosh said:
here is the full number 6:

6. An object is dropped from a height and falls for several seconds.
Which of the following
statements can be true at some time during the fall.

a. Its velocity is more than its acceleration.
b. Its velocity is less than its acceleration.
c. Its velocity is the same as its acceleration.
d. All of the above can be true. (But not at the same exact time)
e. None of the above can be true for a falling object
The thing is, velocity and acceleration have different units. [itex]m/s \neq m/s^{2}[/itex], even if the value of each is the same. What the question should measure (in order for [d] to be correct) are the values of velocity and acceleration.
 
Last edited:
  • #10
wakejosh said:
well i know it can't be B so it must be D, and that makes sense when i run a few numbers through it.
Umm... why can't it be (b)? It is [itex]x^{2}[/itex], right?
 
  • #11
BerryBoy said:
24 - Disagree! The mans rotational energy stays constant i.e:
[tex]\frac{1}{2} I_1 \omega_1^2 = \frac{1}{2} I_2 \omega_2^2[/tex]

So the factor it changes by is:
[tex]\frac{\omega_1^2}{\omega_2^2}[/tex]

not [tex]\frac{\omega_1}{\omega_2}[/tex]

Apart from that, looks good! :smile:

Regards,
Sam

isnt the skater doing work on the system by pulling in his/her arms? and none of my choices are 0, my choices are:

a. 2.4 b. 1.0 c. 0.42 d. 0.25 e. 0.12
 
  • #12
wakejosh said:
here is the full number 6:

6. An object is dropped from a height and falls for several seconds.
Which of the following
statements can be true at some time during the fall.

a. Its velocity is more than its acceleration.
b. Its velocity is less than its acceleration.
c. Its velocity is the same as its acceleration.
d. All of the above can be true. (But not at the same exact time)
e. None of the above can be true for a falling object

Technically speaking (as Andrew pointed out), you cannot compare velocity & acceleration, they are completely different. But you have to make a judgement call and decide if the question is asking about the numbers when velocity & acceleration are in S.I. units - Personally I'd put 'e' and appeal if I were marked wrong.

Regards,
Sam
 
  • #13
geoffjb said:
Umm... why can't it be (b)? It is [itex]x^{2}[/itex], right?


hmm.. you know I don't know for sure. this was emailed to me so I don't know if its supposed to be X*2 or X^2 ... any guesses on what he is looking for here?
 
  • #14
wakejosh said:
isnt the skater doing work on the system by pulling in his/her arms? and none of my choices are 0, my choices are:

a. 2.4 b. 1.0 c. 0.42 d. 0.25 e. 0.12

:uhh: Of course he is! I'm talking absolute rubbish this morning; sorry.

But I don't know if I'd choose 2.4 or 0.42, since [itex]2.4 \times 2.5 = 6[/itex]
 
  • #15
wakejosh said:
hmm.. you know I don't know for sure. this was emailed to me so I don't know if its supposed to be X*2 or X^2 ... any guesses on what he is looking for here?
Based on mathematical custom, I would guess he meant [itex]x^{2}[/itex]. Typically, one would write [itex]2x[/itex] (constant first) when simply multiplying. Fortunately, there is no answer that would be correct if it was [itex]2x[/itex]. That leaves only one choice.
 
  • #16
wakejosh said:
hmm.. you know I don't know for sure. this was emailed to me so I don't know if its supposed to be X*2 or X^2 ... any guesses on what he is looking for here?
By the look of the answers, my money would be on [itex]x^2[/itex], making (b) a nice candidate.

Anyone else?
 

1. How can I know if I did my experiment correctly?

The best way to know if you conducted your experiment correctly is to follow the scientific method. This includes making a hypothesis, designing a controlled experiment, collecting and analyzing data, and drawing conclusions based on the results.

2. What if my results don't match my hypothesis?

This is a common occurrence in science and does not necessarily mean that you did something wrong. It could be due to factors that you did not account for or unexpected variables. It's important to carefully analyze your data and consider alternative explanations.

3. How do I know if my equipment and materials were suitable for the experiment?

Before conducting your experiment, it's important to carefully select and prepare your materials and equipment. Make sure they are appropriate for the experiment and follow any instructions or guidelines provided by the manufacturer. You can also perform a test run to ensure everything is working properly.

4. Should I repeat my experiment multiple times?

Repeating an experiment multiple times can help increase the reliability of your results. This can help account for any errors or inconsistencies that may occur. However, it's important to carefully plan and design each repetition to avoid introducing bias or altering the results.

5. What if I make a mistake during my experiment?

Mistakes can happen during any experiment, and it's important to acknowledge and address them. If the mistake is minor, you may be able to continue with the experiment and make note of the error in your data. If it significantly affects the results, it may be necessary to start the experiment over or make adjustments to your methodology.

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