Final Exam Q6: Finding Problem with Torque Equation

[Alt+F4]

Okay so for a problem, say i wana find how far must u bring ur hands across the string to get a frequency of 350. How would u go about solving that

 

[Doc Al]

A satellite is in circular orbit at a fixed radius from the center of the Earth and with a constant speed. Which one of the following statements is correct about the satellite?

(a) The acceleration is constant but the velocity is not.
(b) Both the acceleration and the velocity are constant.
(c) Neither the acceleration nor the velocity are constant.


Ans:C


WHy so? Constant Speed = Constant Velocity

Careful! Velocity and acceleration are both vectors--direction counts.

 

[Alt+F4]

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam2/sp99 Question 18

(5)(6) + (2) ( 20) - (x)(25) = 0

X = 2.8 why is it 2

 

[Alt+F4]

well

Px = 0
Py = 0

 

[Doc Al]

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam2/sp99 Question 18

(5)(6) + (2) ( 20) - (x)(25) = 0

X = 2.8 why is it 2

First things first. Momentum is a vector. Start by finding the total momentum of the 5-kg and 2-kg pieces.

 

[Alt+F4]

okay so Total Mom = (5)(6) for X, For Y it is (2)(20)

so for X = 30
so for Y = 40

so the vecotr of the third one

u get an angle of 53.13

 

[Doc Al]

okay so Total Mom = (5)(6) for X, For Y it is (2)(20)

so for X = 30
so for Y = 40

so the vecotr of the third one

u get an angle of 53.13

So what's the magnitude of the total momentum (of those two pieces)?

 

[Alt+F4]

50 = MV
got it thanks

 

[Alt+F4]

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam2/sp04

Question 22

15*9.8*50 / 80 = 91.8 ~92

What exactly is the formula since i don't get why you do that, i just have it memorized Why multiply by radii?

 

[Doc Al]

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam2/sp04

Question 22

15*9.8*50 / 80 = 91.8 ~92

What exactly is the formula since i don't get why you do that, i just have it memorized Why multiply by radii?

For the cylinder to be in equilibrium, the torques must balance. Torque depends on the moment arm.

 

[Alt+F4]

Okay i need this straighen out before exam, An elevator going downward say it is Accelerating. Does that Mean Acc is - or is it postive?

So can u just explain to me When say Gravity is negative etc..


Does - Acceleration mean that ur slowing down? Deacc

 

[Beeza]

Okay i need this straighen out before exam, An elevator going downward say it is Accelerating. Does that Mean Acc is - or is it postive?

So can u just explain to me When say Gravity is negative etc..


Does - Acceleration mean that ur slowing down? Deacc

Think about it this way. In general, g is only the magnitude of the acceleration in the y direction. Or, a_y=a_/smallfreefall=-g
Now, this is true when you choose the positive y-direction to point vertically upward. It is a_y that is negative, not g. Does that help?

 

[Doc Al]

Okay i need this straighen out before exam, An elevator going downward say it is Accelerating. Does that Mean Acc is - or is it postive?

Acceleration is the rate of change of velocity. It's a vector and has direction. Calling acceleration + or - is just a sign convention to indicate direction. Usually, + means up and - means down. Note that acceleration and velocity are not necessarily in the same direction. Just because the elevator is moving down, doesn't mean it's acceleration is downward. (It could be slowing down, for instance.)

So can u just explain to me When say Gravity is negative etc..

All that means is that the force of gravity (and the acceleration due to gravity) acts downward, the negative direction.

Does - Acceleration mean that ur slowing down?

Not at all. Acceleration just means that your velocity is changing. Toss a ball straight up into the air. The acceleration is always downward (negative). As the ball rises, it slows; as it falls, it speeds up. But it's always accelerating down.

"Deacceleration" is a confusing term; I would avoid it. (It sometimes is used to mean "slowing down", but it's more helpful to say that your acceleration is negative (compared to your velocity).)

Note that you can have acceleration without speeding up or slowing down. (Think circular motion.)