Q20. Which physical quantity has the same SI unit as pressure?
[UPSC NDA-I GAT – 2017]
A. Stress
B. Angular momentum
C. Strain
D. Work
Answer: A. Stress
Explanation: Stress is force per unit area within a material, and pressure is normal force per unit area. Both are therefore measured in pascals. Strain is dimensionless, angular momentum uses kg m²/s, and work uses joules.
EXAM YEAR 2016
Q19. What is the dimensional formula of dynamic viscosity?
[RPSC Assistant Engineer (DLB) – 2016]
A. [ML⁻¹T⁻¹]
B. [MLT⁻¹]
C. [M⁻¹LT⁻¹]
D. [ML⁻²T⁻²]
Answer: A. [ML⁻¹T⁻¹]
Explanation: Dynamic viscosity relates shear stress to the velocity gradient. Stress has dimensions [ML⁻¹T⁻²], while the velocity gradient has [T⁻¹]. Dividing stress by the gradient gives [ML⁻¹T⁻¹], matching the SI unit pascal-second.
Q18. Which among these is NOT a unit of heat or heat energy?
[MPPSC Prelims – 2016]
A. Calorie
B. Kilocalorie
C. Kilojoule
D. Watt
Answer: D. Watt
Explanation: Calorie, kilocalorie and kilojoule are all measures of energy, including heat. Watt instead measures power, or energy transferred per second. A heater rated at 1,000 watts supplies 1,000 joules each second, not 1,000 joules in total.
Q17. What is the SI unit for mechanical energy?
[UPSC CDS General Knowledge – 2016]
A. Newton
B. Joule
C. Watt
D. Pascal
Answer: B. Joule
Explanation: Mechanical energy includes kinetic and potential energy and is measured in joules. A joule is kg m² s⁻². Newton measures force, watt the rate of energy transfer, and pascal pressure. Correct dimensions settle the choice.
EXAM YEAR 2015
Q16. Which is the SI unit of thermal conductivity?
[UPSC NDA-II GAT – 2015]
A. W·m⁻¹·K⁻¹
B. J·kg⁻¹·K⁻¹
C. W·m·K
D. J·m⁻²
Answer: A. W·m⁻¹·K⁻¹
Explanation: Thermal conductivity relates heat-transfer rate per area to a temperature gradient. Fourier’s law gives units W/(m K), or W m⁻¹ K⁻¹. Joules per kilogram-kelvin denote specific heat capacity, a fundamentally different thermal property.
Q15. Which of the following is NOT a unit of time?
[UPPSC Assistant Conservator of Forests – 2015]
A. Second
B. Minute
C. Light-year
D. Hour
Answer: C. Light-year
Explanation: A light-year is the distance light travels through vacuum in one year, approximately 9.46 × 10¹⁵ metres. Its name mentions a year, but it describes length. Seconds, minutes and hours are all genuine units of elapsed time.
EXAM YEAR 2014
Q14. The dimensions of impulse are identical to those of which quantity?
[UPSC NDA-II GAT – 2014]
A. Energy
B. Linear momentum
C. Pressure
D. Power
Answer: B. Linear momentum
Explanation: Impulse equals force multiplied by the time interval during which it acts. Thus its dimensions are [MLT⁻¹], precisely those of linear momentum. The impulse–momentum theorem states that net impulse equals the change in momentum.
Q13. How many cubic centimetres make one cubic metre?
[UPSC NDA (NA) GAT – 2014]
A. 10³
B. 10⁶
C. 10⁹
D. 10¹²
Answer: B. 10⁶
Explanation: One metre equals 100 centimetres. A volume conversion requires cubing the length conversion factor: (100)³ equals 1,000,000. Thus one cubic metre contains 10⁶ cubic centimetres, not merely 100 cubic centimetres.
EXAM YEAR 2013
Q12. Which physical quantity and unit pairing is INCORRECT?
[UP Lower Subordinate Services Prelims – 2013]
A. Work — joule
B. Force — newton
C. Mass — kilogram
D. Pressure — dyne
Answer: D. Pressure — dyne
Explanation: Dyne is a CGS unit of force, not pressure. In SI the unit of pressure is pascal, equal to N/m². Work in joules, force in newtons and mass in kilograms are all correctly matched quantities and units.
Q11. A light-year is used to measure which kind of quantity?
[UPPSC Review Officer/Assistant Review Officer Prelims – 2013]
A. Astronomical distance
B. Duration
C. Speed of light
D. Luminous intensity
Answer: A. Astronomical distance
Explanation: The distance travelled by light in vacuum over one year is called one light-year. Astronomers use it because interstellar separations are enormous when stated in kilometres. It measures length, while luminous intensity is measured in candelas.
