## Wednesday, April 08, 2009

### [Physics Form 4] Useful Units

1. Why are units important in the measurement of a quantity?
They provide the exact size of the quantity measured; they provide information about the type of quantity measured; they allow for comparisons between two measurements of the same quantity.

2. State the SI units of the following quantities: electric current, velocity, acceleration, mass, time, energy, pressure, work, momentum and weight.
Electric current: A
Velocity: ms-1
Acceleration: ms-2
Mass: kg
Time: s
Energy: J
Pressure: Pa
Work: J
Momentum: kgms-1
Weight: N

3. Differentiate between the SI unit and the SI base unit of force.
The SI unit of force is N (Newton) while the SI base unit of force is kgms-2

4. Are cm and m base unit? Differentiate them.
Yes, both are base units of length, a base quantity. However cm is not the SI unit of length while m is.

5. State the value equivalent of 1m2 and 1cm3 , respectively.
1m2 = 1 x 104 cm2
1cm3 = 1 x 10-6 m3

6. How fast is a car moving in ms-1 if its speed is 72kmh-1 ?
72kmh-1 = 72km / 1h
= (72 x 103 m) / (3.6 x 103 s)
= 20ms-1