Weird physics questions

Okay, I had an idea of what this stupid question was asking for..however, i thought it was too basic that i didnt really know how to frame the answer..
So my question is , how would you answer the following questions

Number 1: With the aid of an example , explain the statement, "The magnitude of a physical quantity is written as the product of a number and a unit".

Number 2: Explain why an equation must be homogeneous with respect to the units , if it is to be correct

How would you answer this question.. Please I would like to get different diverse responses to this...THANKS GUYS...

Anyone?????

Anyone?????

First one, 3ms^-2, a number and unit
Second one, E = hf, E= (mv^2)/2, E = hc/lamba etc, all energy equations and need to be homogeneous otherwise they can't be used

Nice questions

teachercol

Nice questions

Well, the questioner has clearly forgotten that not all quantities have an associated unit. Refractive Index and Coefficient of Restitution for example.

Reply 6

VagnTheBrave

int_applicant

Number 1: With the aid of an example , explain the statement, "The magnitude of a physical quantity is written as the product of a number and a unit".

A Unit must be given, otherwise a quantity doesn't make sense for physical measurements, for example, say you could measure a building to be 100m and don't put a unit, then anyone else wouldn't know whether it was 100m, 100 feet, or even 100 lightyears, so it is done so that other people know what you are talking about.

Number 2: Explain why an equation must be homogeneous with respect to the units , if it is to be correct

Any equation must have equal units on each side of the equation, just as the numbers must be equal, so must the units, otherwise the two parts of the equation are not equal.

For example, E=mc^2 , the joule is defined as 1kg m^2/s^2, obviously this is the case here.

Reply 7

int_applicant

Stonebridge

Well, the questioner has clearly forgotten that not all quantities have an associated unit. Refractive Index and Coefficient of Restitution for example.

Those are not physical quantities....

Any other potential answers from anyone?

Reply 8

Stonebridge

Originally Posted by Stonebridge
Well, the questioner has clearly forgotten that not all quantities have an associated unit. Refractive Index and Coefficient of Restitution for example.

int_applicant

Those are not physical quantities....

Any other potential answers from anyone?

They are dimensionless quantities.
http://en.wikipedia.org/wiki/Dimensionless_quantity

BTW. The "questioner" I referred to was not you, but the writer of the original question in the book or exam.

(edited 13 years ago)

Reply 9

int_applicant

Stonebridge

Originally Posted by Stonebridge
Well, the questioner has clearly forgotten that not all quantities have an associated unit. Refractive Index and Coefficient of Restitution for example.

They are dimensionless quantities.
http://en.wikipedia.org/wiki/Dimensionless_quantity

BTW. The "questioner" I referred to was not you, but the writer of the original question in the book or exam.

oh..its okay mate,.... I knew you weren't talking to me...

I suppose I was just trying to point out that the response you gave wasn't applicable to the question because the examples you gave were not physical quantities ( as you have rightly pointed out).. Consequently, the answer wasn't applicable... The question is asking about physical quantities..

Cheers though.... :thumbsup:

Reply 10

Stonebridge

It's getting a bit confusing here.
I was not responding to your original post, but to TeacherCol's remark (post #5) that the original questions you asked about were "nice".
My point was that the 1st question assumes that all physical quantities have a magnitude and a unit.
When I pointed out that the two examples I gave were "dimensionless quantities", I was not saying they were not physical quantities. Quite the opposite. They are examples of physical quantities that have no units. These are normally the result of units cancelling out because they represent a ratio between two quantities having equal units.
The point I was making has got somewhat lost in the confusion.
Vagn's reply (#7) is fine.
An equation, if it is to be equal on both sides, must have equal magnitudes and equal units.
After all 5 miles is not equal to 5 kilometers. The magnitudes are equal but not the units.