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Friday, May 1, 2020

Complete Fig 1.1 to show each quantity and its unit.


Question 15
Complete Fig 1.1 to show each quantity and its unit. [4]

            Quantity                                  Unit
            speed                                       m s-1
            density                       
                                                            s-1
            electric field strength             
                                                            kg m s-1





Reference: Past Exam Paper – June 2003 Paper 2 Q1





Solution:
Quantity                                  Unit
            speed                                       m s-1
            density                                    kg m-3
            frequency                               s-1
            electric field strength              N C-1 or V m-1 or kg m s-2 C-1
            momentum or impulse          kg m s-1

{The unit of density is kg m-3 (= mass / volume).

A unit of s-1 means that the quantity is ‘something divided by time’. The numerator should not have any unit. This could be frequency (= 1 / period) or count rate or activity or decay constant.

The question has NOT asked for the SI BASE unit. So, the unit of electric field strength can be given as N C-1 (= force / charge) or V m-1 (= p.d. / distance) or in SI base units, kg m2 C-1. However, there was no need to convert into SI base unit as this was not specified in the question.

In the unit kg m s-1, kg is the unit of mass and m s-1 is the unit of velocity. The quantity represented by ‘mass × velocity’ is momentum (or impulse).}

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