# Clock problem involving displacement

1. Jan 2, 2010

### halenb

1. The problem statement, all variables and given/known data
the minute hand of a wall clock measures 10 cm from its tip to the axis about which it rotates. the magnitude and angle of the displacement of the tip are to be determined for three time intervals. what are a) magnitude and b) angle from a quarter after the hour to half past, the c) magnitude and d) angle for the next half hour and the e) magnitude and f) angle for the hour after that

2. Relevant equations

I'm not sure......

3. The attempt at a solution

the only thing I was able to come up with is that for B) i know thats a 90 degree change, D) thats a 180 degree change and F) is a 360 degree change

2. Jan 2, 2010

### pgardn

and...

Angular displacement vs. distance?

3. Jan 2, 2010

### halenb

we haven't really done a lot with radians but we have/are studying angular displacement but not vs distance

4. Jan 2, 2010

### pgardn

Let us assume then that your teacher wants magnitude in cm or meters.

The hand of a clock is really the radius of a circle if the tip is considered the point of interest. So how much of a circle does the hand make given your question(s). I think you might have used C = 2(pi)r, yes? for the circumference of a circle? Well if you substitute r = what you were given in the problem for the distance from the middle of the clock to the tip, you have the distance the tip travels if it goes one full revolution or one full circumference.

Now if the hand does not go a full circumference, or revolution, then it goes some part of
2(pi)r...

For example, if the hand moves 90 degrees is this not 1/4 of a circumference or revolution...?
I think you see where I am leading you, yes?

5. Jan 2, 2010

### halenb

yes that makes sense to find the distance it travels but, im still not sure how to find the magnitude of each of them....? do i use the distance to figure that out?

6. Jan 2, 2010

### halenb

or do i just do 10+10+ whatever the distance was

7. Jan 2, 2010

### pgardn

The magnitude is the distance or possibly angular displacement. Magnitude just means an amount without reguard to direction. So it is merely asking about how far did the tip go.

But do you need to put it in cm or radians or both...