Railway Science (Physics-Units and Measurements)

Total Questions: 50

41. Which of the following Physical quantities has no unit ? [RRB Group D 23/09/2018 (Afternoon)]

Correct Answer: (d) Relative density
Solution:

It is a comparative measure of the density of a substance to the density of a reference substance. Standard Units : Momentum - kg-m/s, Density - kg/m³ , Pressure - N/m² , Magnetic Flux - weber, Moment of inertia - kg-m² , Impulse - kg-m/s, Power - kg-m²/s³ .

42. Which of the following pairs have the same units? [RRB Group D 23/09/2018 (Evening)]

Correct Answer: (c) Work and energy
Solution:

Their SI unit is Joule (J). SI units of some other physical quantities : Force and Weight - newton (N), Electric charge - coulomb (C), Frequency - hertz (H), Power and Radiant flux - watt (W), Electric potential - volt (V), Inductance - henry (H), Capacitance - farad (F).

43. The SI unit of pressure is called : [RRB Group D 23/09/2018 (Evening)]

Correct Answer: (d) Pascal
Solution:

Pascal (Pa). SI Units of some other physical quantities : Magnetic flux - weber (Wb), Magnetic flux density - tesla (T), electrical inductance - henry (H), luminous flux - lumen (lm), Angle - radian (rad), Radioactivity - becquerel (Bq).

44. The SI unit of __________ is Newton. [RRB Group D 01/10/2018 (Morning)]

Correct Answer: (b) weight and force
Solution:

Weight is just another word for the force of gravity (W = mg). Force makes things move or, more accurately, makes things change their motion. Two natural forces are the force of gravity and magnetic forces. Force is a vector quantity.

45. Which of the following pairs do not have same SI unit? [RRB Group D 01/10/2018 (Evening)]

Correct Answer: (b) Force and pressure
Solution:

SI Units of some Physical Quantities: Force (Newton), Pressure (Pascal), Distance and Displacement (Meter), Energy and Work (Joule), Speed and Velocity (Metre per second). Seven fundamental quantities and their SI Unit: Length (metre), Mass (kilogram), Time (second), Electric Current (ampere), Thermodynamic temperature (kelvin), Amount of substance (mole), Luminous intensity (candela).

46. The SI unit of 'g' is same as that of acceleration, that is_________ [RRB Group D 03/10/2018 (Afternoon)]

Correct Answer: (b) ms⁻²
Solution:

Here ‘g’ is acceleration due to gravity on Earth. Value of ‘g’ is 9.8 m/s² . The acceleration due to gravity has both the magnitude as well as direction. Hence, it is a vector quantity. Other SI units : Length - meter (m), Time - second (s), Amount of substance - mole (mole), Electric current - Ampere (A), Temperature - Kelvin (K), Mass - kilogram (kg).

47. What does a light year measure? [RRB Group D 03/10/2018 (Afternoon)]

Correct Answer: (b) Distance
Solution:

Light-year is the distance light travels in one year {5.88 trillion miles (9.46 trillion kilometers)}. 1 light year = 9.46 × 10¹⁵ m = 9.46 × 10¹² km = 9.46 × 10¹⁷ cm. Other SI units : velocity - meter per second (m/s), Energy - joules (J), Power - Watt (W), Electric current - Ampere (A), Temperature - Kelvin (K), Mass - kilogram (kg).

48. Which of the following pairs have the same SI units? [RRB Group D 03/10/2018 (Afternoon)]

Correct Answer: (c) Work and energy
Solution:

The seven SI base units - Length - Meter (m), Time - Second (s), Amount of substance - Mole (mole), Electric current - Ampere (A), Temperature - Kelvin (K), Luminous intensity - Candela (cd), Mass - Kilogram (kg).

49. The international (SI) unit of retardation is _________. [RRB Group D 03/10/2018 (Evening)]

Correct Answer: (d) m𝑠⁻²
Solution:

Retardation is the total opposite of acceleration i.e., negative acceleration.

50. The SI unit of _______ is Ohm. [RRB Group D 04/10/2018 (Morning)]

Correct Answer: (d) resistance
Solution:

SI Units of some other physical quantities : Force and Weight - newton, Frequency - hertz, Electric charge - coulomb, Electric potential - volt, Inductance - henry, Capacitance - farad, Electrical conductance - siemens, RadioactivityBecquerel.