Physics Objective (Multiple Choice) General Knowledge & General Science Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examinations.

21.The minimum speed required to put a satellite into a given orbit around earth is known as:

[A] Escape velocity

[B] Orbital velocity

[C] Kinetic velocity

[D] None of the above

**Correct Answer:** B [Orbital velocity]

**Notes:**

The minimum speed required to put a satellite into a given orbit around earth is known as Orbital velocity of the satellite. Orbital velocity (v) = (GM/r)^{1/2} where G= gravitational constant, M= mass of the earth and r = radius of the orbit of the satellite.

22.If the time of revolution is T in a satellite, then kinetic energy is proportional to which of the following:

[A] T^{-4/3}

[B] T^{2/3}

[C] T^{-2/3}

[D] T^{-1/3}

**Correct Answer:** C [T^{-2/3}]

**Notes:**

The square of the period of any planet is proportional to the cube of the semimajor axis of its orbit. So r is inversely proportional to cube root of the square of T. And Kinetic energy is inversely proportional to r. Therefore, K.E is directly proportional to (T)^{-2/3}

23.By how much the orbital velocity of Moon has to increase for it to cease to remain the earth’s satellite?

[A] 2 times

[B] 3 times

[C] √2 times

[D] √3 times

**Correct Answer:** C [√2 times]

**Notes:**

If the speed of a satellite orbiting close to the earth is made √2 times (or increased by 41%) then it will escape from the gravitational field. Moon is a natural satellite of earth.

24.What is the S.I unit of Pressure?

[A] N/Kg m^{2}

[B] N/m

[C] N/m^{3} s

[D] N/m^{2}

**Correct Answer:** D [N/m^{2}]

**Notes:**

The SI unit of pressure is N/m^{2} It has been named as Pascal (Pa) in honour of the French scientist Blaise Pascal for carrying out pioneering studies on fluid pressure. Its dimensions are M L^{-1}T ^{-2}

25.What will be the buoyant force acting on the stone, on being immersed in water, if it displaces 100gms of water?

[A] 1000 gm-weight

[B] 100 gm-weight

[C] 10 gm-weight

[D] 1 gm-weight

**Correct Answer:** B [100 gm-weight]

**Notes:**

As per Archimedes’ principle, if a stone, on being immersed in water, displaces 100gms of water, the buoyant force acting on the stone will be equal to 100gm-weight.

26.What is the difference of pressure between two sides of the liquid surface called as?

[A] Excess Pressure

[B] Surface Pressure

[C] Fluidic Tension

[D] Viscosity

**Correct Answer:** A [Excess Pressure]

**Notes:**

In equilibrium the pressure inside a bubble or drop is more than the pressure outside. The difference of pressure between two sides of the liquid surface is called as excess pressure.

27.What is the unit of surface tension in c.g.s system?

[A] N/m

[B] dyne/cm

[C] erg/cm

[D] dyne cm

**Correct Answer:** B [dyne/cm]

**Notes:**

The unit of surface tension is S.I system is N/m and in c.g.s system is dyne/cm. It is represented by T = force/length.

28.What is the angle of contact for pure water and glass?

[A] 0°

[B] 30°

[C] 180°

[D] 90°

**Correct Answer:** A [0°]

**Notes:**

Angle of contact between a liquid and a solid is defined as the angle enclosed between the tangents to the liquid surface and the solid surface inside the liquid, both the tangents being drawn at the point of contact of the liquid with the solid. Its value lies between 0° and 180°: 0°for pure water and glass, 8°for tap water and glass, 90° for water and silver

29.What is the oscillation known as if it can be expressed in terms of single harmonic function?

[A] Harmonic oscillation

[B] Functional oscillation

[C] Regular oscillation

[D] None of the above

**Correct Answer:** A [Harmonic oscillation]

**Notes:**

Harmonic oscillation is that oscillation which can be expressed in terms of single harmonic function (i.e. sine or cosine function). Example :y =asin w t or y = acos w t

30.Which of these is a physical quantity which completely express the position and direction of motion of the particle?

[A] Frequency

[B] Displacement

[C] Phase

[D] Time period

**Correct Answer:** C [Phase]

**Notes:**

Phase of a vibrating particle at any instant is a physical quantity, which completely express the position and direction of motion, of the particle at that instant with respect to its mean position.