# Units and Measurement

### Question:

(a) The earth-moon distance is about 60 earth radius. What will be the diameter of the earth (approximately in degrees) as seen from the moon?
(b) Moon is seen to be of (1/2) ° diameter from the earth. What must be the relative size compared to the earth?
(c) Fronj parallax measurement, the sun is found to be at a distance of about 400 times the earth-moon distance. Estimate the ratio of sun-earth diameters.

### Units and Measurement

#### Q 2.

Why length, mass and time are chosen as base quantities in mechanics?

#### Q 6.

Why do we have different units for the same physical quantity?

#### Q 7.

Name the device used for measuring the mass of atoms and molecules.

#### Q 8.

Which of the following time measuring devices is more precise?
(a) A wall clock (b) A stop Watch (c) A digital watch (d) An atomic clock

#### Q 9.

The vernier scale of a travelling microscope has 50 divisions which coincide with 49 main scale divisions. If each main scale division is 0.5 mm, calculate the minimum inaccuracy in the measurement of distance.
Thinking Process
Inaccuracy will be measured by difference of 1 MSD and 1VSD, where MSD = mam scale division and VSD = verneir scale division.

#### Q 10.

Which of the following measurement is most precise?
(a) 5.00 mm (b) 5.00 cm (c) 5.00 m (d) 5.00 km

#### Q 11.

Express unified atomic mass unit in kg.

#### Q 15.

(a) The earth-moon distance is about 60 earth radius. What will be the diameter of the earth (approximately in degrees) as seen from the moon?
(b) Moon is seen to be of (1/2) ° diameter from the earth. What must be the relative size compared to the earth?
(c) Fronj parallax measurement, the sun is found to be at a distance of about 400 times the earth-moon distance. Estimate the ratio of sun-earth diameters.

#### Q 16.

(a) The earth-moon distance is about 60 earth radius. What will be the diameter of the earth (approximately in degrees) as seen from the moon?
(b) Moon is seen to be of (1/2) ° diameter from the earth. What must be the relative size compared to the earth?
(c) Fronj parallax measurement, the sun is found to be at a distance of about 400 times the earth-moon distance. Estimate the ratio of sun-earth diameters.

#### Q 17.

The length and breadth of a rectangular sheet are 16.2 cm and 10.1 cm, respectively. The area of the sheet in appropriate significant figures and error is
(a) 164 ± 3 cm2 (b) 163.621 2.6 cm2 (c) 163.61 2.6 cm2 (d) 163.621 3 cm2

#### Q 18.

The radius of atom is of the order of 1 A and radius of nucleus is of the order of fermi. How many magnitudes higher is the volume of atom as compared to the volume of nucleus?