# 20 Amazing Questions of Physics Science

##### 20 Amazing Questions of Physics Science

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PHYSICAL QUANTITIES WITH NATURE

 Physical Quantity Symbol Nature Unit Speed v Scalar m/s Velocity v Vector m/s Acceleration a Vector m/s2 Acceleration due to gravity g Vector m/s2 or N/Kg Mass m Scalar Kg Weight W Vector Kg-m/s2 or N Force F Vector Kg-m/s2 or N Torque or moment of force or couple T Vector N-m Work W Scalar Kg m2/s2 or J Mechanical Advantage MA —— —— Velocity ratio VR —– —– Energy E Scalar Kg m2/s2 or J or Nm Kinetic energy KE or EK Scalar Kg m2/s2 or J or Nm Potential energy PE or U Scalar Kg m2/s2 or J or Nm Power P Scalar Kg m2/s3 or J/s or Nm/s or W
##### 20 Amazing Questions of Physics Science

IMPORTANT QUESTIONS

(1) What do you mean by kilogram force and write its relation with newton?

Answer: One kilogram force (kg f) is the force required to lift a body of mass 1 kilogram.

1 kg f = 9.8 N

(2) Give a few examples of couple.

Answer: Rotation of an object is due to couple.

Few examples of couple are: turning a water tap, tightening of the cap of an inkpot, winding a clock with the key, steering of a four wheeler, driving the pedal of a bicycle, opening of a door etc.

(3) Which type of motions are exhibited by a vehicle and its wheels?

Answer: The motion of vehicle is translatory and the motion of wheels is rotatory.

(4) What do you mean by axis of rotation?

Answer: Axis of rotation is the line or point about which the object rotates. It may be within the object or outside the object.

(5) What do you mean by an ideal or perfect machine?

Answer: Ideal or perfect machine means the machine whose parts are weightless and frictionless such that whatsoever amount of energy is spent on it, the same amount of energy is produced by it.

(6) Why can a machine not be 100% efficient?

Answer: A machine cannot be 100% efficient because a part of input is

(a) wasted in moving the parts of the machine.

(b) in overcoming friction between different parts of machine.

(7) Which class of levers has a mechanical advantage always less than one?

In third class of levers, effort arm is always less than load arm therefore mechanical advantage is always less than 1.

Example of class III lever is sugar tongs.

(8) Define Driving gear.

Answer: Driving gear is the gear closer to the source of power.

(9) Define Driven gear.

Answer: Driven gear is the gear wheel which receives motion from the driver.

(10) Define Gain in speed.

Answer: This is the ratio of speed of rotation of driven wheel to the speed of rotation of driving wheel.

(11) Define Gain in torque.

Answer: This is the ratio of the number of teeth in driven gear to the number of teeth in driving gear.

(12) When do the two gears rotate in the same direction or in the opposite direction?

Answer: If two gears make external contact, both rotate in the opposite direction i.e. driven gear rotates in the opposite direction to the driving gear.

If two gears make internal contact, both rotate in the same direction i.e. driver gear and driven gear rotate in the same direction.

(13) State the condition when there is neither gain in torque nor gain in speed.

Answer: If number of teeth on driving gear is equal to the number of teeth on driven gear, there will neither be gain in torque nor gain in speed.

(14) How do you measure the work when the force is applied at an angle?

Answer: If the force is applied at an angle α with the horizontal surface and the body is displaced along the surface, work done is the product of the component of the force (F cos α) along the direction of the displacement and the displacement of the body, i.e.

W = Fs cos α

(15) What should be the angle between force and displacement to get the work (a) maximum (b) minimum?

Answer: We know that, W = Fs cos α

(a) If α = 0 degree, i.e. the angle between the force F and the displacement s in the same direction is zero.

W = Fs cos 0

W = Fs (cos 0 degree = 1)

(b) If α = 90 degree, i.e. the force under consideration is normal to the direction of motion.

W= Fs cos 90

W = 0 (cos 90 degree = 0)

 Give an example in which force does no work on the body.

Answer: When a body is whirled around in a circle with uniform speed, e.g. a stone tied to the end of a string. The force is directed towards the centre and always normal to the direction of motion. Hence the work done is zero. [W = Fs cos 90] = 0

 State SI and CGS units of work.

Answer: SI unit of work is joule. Work is said to be one joule if a force of one newton displaces a body one metre in its own direction. Thus,

1 joule [J] = 1 newton [N] × 1 metre [m]

CGS unit of work is erg. Work is said to be one erg if a force of 1 dyne displaces its point of application through one centimeter in its own direction. Thus,

1 erg = 1 dyne × 1 cm

 Write the circumstances in which work done by a force is zero.

Answer: Amount of work done by a force is zero when

[a] There is no displacement or

[b] The displacement is normal to the direction of the force.

 Does a coolie carrying load on his head do any work while standing or while moving? If not why?

He does no work against the force of gravity while moving on the ground since displacement is normal to the force of gravity.

 Select the scalar quantities from the following: Volume, Momentum, Force, Work, Energy, Acceleration, Kinetic Energy, Velocity, Potential Energy, Power and Displacement.

Answer: Volume, Work, Energy, Kinetic Energy, Potential Energy and Power.

##### 20 Amazing Questions of Physics Science

KEY POINTS:

(1) law of conservation of energy

(2) Transformation of energy

(3) Kinetic energy

(4) Potential energy

(5) renewable source of energy

(6) Non-renewable sources of energy

(7) Nuclear energy and Geothermal energy

(8) Wind energy

(9) Tidal energy

(10) Ocean thermal energy

##### (1) According to the law of conservation of energy, it can neither be created nor destroyed. It can only be changed from one form to another. Thus, the total energy before and after the transformation always remains constant. (2) Transformation of energy is the conversion of energy from one form to the other.

(3) Energy is found in various forms such as mechanical energy, chemical energy, heat energy, elastic energy, sound energy, light energy, electrical energy, nuclear energy, etc.

##### 20 Amazing Questions of Physics Science (4) Mechanical energy is of two types.

(a) Kinetic energy

(b) Potential energy

(5) Kinetic energy is the energy possessed by an object by virtue of its motion. Its expression is

Kinetic Energy (KE) = ½ m v2

Where m is the mass of the object and v is the velocity attained by the object.

##### 20 Amazing Questions of Physics Science ALL SUBJECTS

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(6) Potential energy is the energy possessed by an object due to its position. Its expression is

Potential Energy (PE) (U) = mgh

Where m is the mass of the object, g is the acceleration due to gravity and h is the height.

(7) The main source of energy on the earth is the Sun which is radiating an enormous amount of energy at the present rate for nearly 5 billion years and will continue radiating at the same rate for about more than 5 billion years.

The energy stored in the coal, petroleum products, wood, air and ocean currents, clouds and rain are all derived from the sun.

(8) Sources of energy can be classified as renewable sources and non-renewable sources.

(9) A renewable source of energy provides energy in a convenient form over a long period of time.

##### 20 Amazing Questions of Physics Science

(10) Renewable sources of energy can be used again and again.

Examples : Sun energy, energy of the flowing water, wind energy, tidal energy, ocean waves energy.

(11) Non-renewable sources of energy are those which cannot be used again and again i.e. once used, are exhausted. Examples: fossil fuels like coal, petrol, natural gas, diesel etc.

(12) The energy harnessed from flowing water, wind, tides ocean waves and biogas are the energy sources that are directly or indirectly derived from the energy of the sun.

(13) Nuclear energy and Geothermal energy are examples of other sources of energy but are likely to be available for a long time. These are not related to Sun’s energy. Those source of energy are also classified as renewable sources.

##### 20 Amazing Questions of Physics Science

(14) Energy of water flowing through rivers is also solar energy in another form. It is utilized to produce electricity on a large scale at hydroelectric power plants.

(15) Wind energy is an environment friendly and efficient source of renewable energy which requires no recurring expenses for the production of electricity.

Energy harnessed through wind energy devices is used :

(a) to do mechanical work

(b) to produce electricity

(16) Tidal energy is the energy possessed by the rising and falling water in tides.

(17) Waves generated by strong winds blowing across the sea possess kinetic energy which can be trapped to generate electricity.

##### 20 Amazing Questions of Physics Science

(18) Geothermal is the energy derived from the hot spots beneath the earth.

Geothermal energy is the heat energy present inside the earth’s crust.

It occurs in three forms: natural regions, hot water and hot rocks.

(19) Ocean thermal energy is the energy harnessed due to temperature difference (20 degree Celsius or more) between warm surface waters heated by the sun and colder waters found at ocean depths upto 2 km. The devices used to harness this form of ocean energy are known as Ocean Thermal Energy Conversion (OTEC) power plants. It is another form in which solar energy becomes available from the oceans.

(20) Energy of flowing water, tides and ocean waves is harnessed to produce electricity by building dams.

##### 20 Amazing Questions of Physics Science

(21) Photosynthesis is the process in which green plants convert solar energy into chemical energy. This energy is known as bioenergy.

(22) In a thermal power plant, fossil fuels (coal, petroleum and natural gas) are burnt to heat up water to produce steam which further runs turbine to generate electricity. Hence heat energy is converted into electrical energy.

(23) Hydropower plants convert the potential energy of falling water into electricity. Since there are very few water walls which could be used as a source of potential energy, hydropower plants are associated with dams.

##### 20 Amazing Questions of Physics Science (24) Solar energy devices used for harnessing solar energy are solar cookers, solar water heaters, solar water pumps and solar photovoltaic cells.

(25) Solar energy devices are broadly classified into two categories on the basis of their principle of working.

(a) In solar cookers and solar water heaters, the solar energy is collected in the form of heat.

(b) In solar cells, the solar energy is converted into electricity.

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