Q60. Which of these is the SI unit of velocity?
[SSC GD Constable – 1 March 2024]
A. kg/m
B. kg/s
C. m/s
D. s/m
Answer: C. m/s
Explanation: Velocity represents displacement divided by elapsed time, so its SI unit is metre per second. The vector character of velocity does not alter its unit. The reciprocal, seconds per metre, is not a velocity unit.
Q59. Which group contains only units of energy?
[SSC Stenographer – 10 December 2024]
A. Joule, newton and calorie
B. Watt, joule and newton
C. Joule, calorie and kilowatt-hour
D. Pascal, joule and watt
Answer: C. Joule, calorie and kilowatt-hour
Explanation: Joule, calorie and kilowatt-hour all quantify energy, although only joule is the coherent SI unit. Newton measures force, watt measures power and pascal measures pressure. Recognising dimensions distinguishes these related but different physical quantities.
EXAM YEAR 2023
Q58. Poundal is a unit associated with which quantity?
[WBCS Mains (Science) – 2023]
A. Mass
B. Weight
C. Momentum
D. Energy
Answer: B. Weight
Explanation: The poundal is a unit of force in the foot-pound-second system. Weight is a gravitational force, making it the suitable choice. One poundal is the force required to accelerate one pound of mass at one foot per second squared.
Q57. Approximately how many metres are represented by one X-unit used in X-ray crystallography?
[WBCS Mains (Science) – 2023]
A. 10⁻¹⁵ m
B. 10⁻¹² m
C. 10⁻¹⁰ m
D. 10⁻¹³ m
Answer: D. 10⁻¹³ m
Explanation: The X-unit was introduced for precise X-ray wavelength and crystal-spacing measurements. Its magnitude is approximately 1.002 × 10⁻¹³ metre. It is much smaller than a nanometre and is not one of the seven SI base units.
Q56. The total ozone in an atmospheric column is expressed using which unit?
[Chhattisgarh PSC Prelims – 2023]
A. Ozone unit
B. Thomson unit
C. Dobson unit
D. None of these
Answer: C. Dobson unit
Explanation: The Dobson unit expresses the amount of ozone in a vertical column of atmosphere. One Dobson unit corresponds to an equivalent pure ozone layer only 0.01 millimetre thick at standard temperature and pressure. It does not express sound or electric current.
Q55. Nephelometric Turbidity Unit (NTU) measures which property of water?
[Rajasthan RAS Prelims – 2023]
A. Water pressure
B. Water temperature
C. Water acidity
D. Water turbidity
Answer: D. Water turbidity
Explanation: NTU quantifies how strongly suspended particles scatter light in a water sample, indicating its turbidity or cloudiness. It is not a measure of pressure, acidity or temperature. Turbidity measurements are commonly used in water-quality monitoring.
Q54. Which SI unit is used for magnetic flux density?
[SSC CGL Tier I – 26 July 2023]
A. Candela
B. Coulomb
C. Tesla
D. Pascal
Answer: C. Tesla
Explanation: The tesla, symbol T, measures magnetic flux density or magnetic induction. One tesla equals one weber per square metre and one newton per ampere-metre. The other options quantify luminous intensity, electric charge and pressure, respectively.
Q53. What is the SI unit of linear momentum?
[SSC MTS – 5 September 2023]
A. kg²·m/s
B. kg·m/s²
C. kg·m²/s
D. kg·m/s
Answer: D. kg·m/s
Explanation: Linear momentum is the product of mass and velocity, p = mv. Kilograms multiplied by metres per second give kg m/s. A kg m/s² corresponds to force, illustrating how an additional inverse second changes the physical dimension.
Q52. Who introduced the horsepower unit, originally equated to about 33,000 foot-pounds of work per minute?
[SSC MTS – 4 September 2023]
A. James Black
B. James Croll
C. James Watt
D. James Dwight Dana
Answer: C. James Watt
Explanation: James Watt popularised horsepower to compare steam engines with the output of working horses. Mechanical horsepower is approximately 746 watts, or 550 foot-pounds of work per second. Horsepower measures power rather than total energy produced.
Q51. Which physical quantity is measured in kilowatt-hours?
[SSC MTS – 3 May 2023]
A. Electric current
B. Force
C. Energy
D. Momentum
Answer: C. Energy
Explanation: A kilowatt-hour results from multiplying kilowatts of power by operating hours. Since power is energy per unit time, the hour cancels the time denominator and leaves energy. It equals 3.6 × 10⁶ joules and is used for electricity consumption.
