Check out some similar questions!

MS_SUMTER2010 · Feb 11, 2010, 01:29 PM

A toy electric train moving at a constant speed on a circular track that has a radius of 1.2 meters goes around the track every 8 seconds.

a) what is the speed of the train?

b) what is the centripetal acceleration of the train?

c) what force turns the train?

ebaines · Feb 11, 2010, 01:34 PM

You need to apply:

a) $v = \omega R$
b) $a = \omega ^2 R$ , or $a = v^2/R$

For both of these you need to calculate $\omega$ , which is the rotational velocity of the train meausred in radians/second. To do that, use: $\omega =2 \pi/T$

As for what force keeps it on the traccks - what do you think?

MS_SUMTER2010 · Feb 11, 2010, 01:37 PM

I don't know what the omega is though so I can't solve it. And the forces I think they are normal force and friction force

MS_SUMTER2010 · Feb 11, 2010, 01:38 PM

Is the speed 0.94 m/s?

ebaines · Feb 11, 2010, 01:40 PM

Originally Posted by MS_SUMTER2010

Is the speed 0.94 m/s?

Yes - very good!

MS_SUMTER2010 · Feb 11, 2010, 01:42 PM

Was my answer for the forces correct? The friction force and the normal force.

ebaines · Feb 11, 2010, 01:47 PM

How does friction cause the train to turn? Friction opposes the direction of motion of an object, so causes it to slow down, not turn (unless you have something weird going on causing uneven resistance - like a car whose brakes only work on the left side). And please clarify what you mean by "normal force" - in this problem you have a normal force between what and what?

MS_SUMTER2010 · Feb 11, 2010, 01:50 PM

Normal force is the perpendicular contact force exerted by a surface on another object. My choices for this answer are:

A) tension in a string
B) force of gravity
C) Friction
D) Normal Force
E) Force in a Sprng
F) Air resistance

It can be more than one. Im just not sure which one.

ebaines · Feb 11, 2010, 02:03 PM

Well, there's no spring ir string in this problem,so those are out. So the question to you is: would gravity, friction, normal force, or air resistance cause a turning motion? Hint - this needs to be a force acting on the train towards the center of the circular track.

MS_SUMTER2010 · Feb 11, 2010, 02:09 PM

I say that there is gravity and air resistance. Am I correct?

MS_SUMTER2010 · Feb 11, 2010, 02:11 PM

And normal force... because of the train and the track

ebaines · Feb 11, 2010, 02:13 PM

EDIT: this answer is in respnse to post #10

Nope. These forces both act on the train all right, but do NOT cause it to turn. Gravity is a force in the downward direction - not towards the center of the circle. Air resistance is a force opposing the diretion the train is moving (along the track) - again not toward the center.

ebaines · Feb 11, 2010, 02:15 PM

Originally Posted by MS_SUMTER2010

and normal force... because of the train and the track

Normal force between the outside edges of the train wheels and the inside edges of the track, right?

MS_SUMTER2010 · Feb 11, 2010, 02:17 PM

Yes! I think that the train has a normal force and a friction force!

ebaines · Feb 11, 2010, 02:19 PM

Why friction?? Think - what direction does friction work in? Does it make the train turn? Or just slow down?

MS_SUMTER2010 · Feb 11, 2010, 02:25 PM

Slow down

ebaines · Feb 11, 2010, 02:27 PM

Originally Posted by MS_SUMTER2010

slow down

Right. So - of all the forces you listed, which one(s) make the train turn?

MS_SUMTER2010 · Feb 11, 2010, 02:29 PM

Ok for example a plane will need friction, gravity and normal force while it is in the air right?

MS_SUMTER2010 · Feb 11, 2010, 02:29 PM

The normal force makes the train turn.

ebaines · Feb 11, 2010, 02:32 PM

Normal forces yes - caused by the force of the air against the tail and wings (assuming the plane is banking as it turns).

As for the other forces - why would either friction or gravity come into play? Same reasooing as with the train - these forces act in the wrong direction!