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Science Do as directed; [1 M ]

Work, Power And Energy · MP Board (MPBSE) STD 9 (Madhya Pradesh - English Medium). 70 questions.

Questions · Page 1 of 2

Do as directed; [1 M ]

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50 questions · timed · auto-graded

Question 11 Mark
Name five appliances or machines which use an electric motor.
Answer
Fan, washing machine, mixer grinder, water pump, hair dryer use electric motor.
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Question 41 Mark
Define average power.
Answer
When a machine or person does different amounts of work or uses energy in different intervals of time, the ratio between the total work or energy consumed to the total time is average power.
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Question 91 Mark
Calculate the work done when a force of $15N$ moves a body by $5m$ in its direction.
Answer
$w = f × s$
$w = 15 × 5$
$w = 75$
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Question 121 Mark
Is work a scalar or a vector quantity.
Answer
Work is a scalar quantity. Work, as a physical quantity, requires only magnitude to be represented. Hence, it is scalar quantity.
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Question 131 Mark
Define $1$ watt of power.
Answer
A body is said to have power of $1$ watt if it does work at the rate of $1$ joule in $1$ s, i.e., $1 W = 1J/1s$.
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Question 141 Mark
Give the formula to calculate work done on an object if force applied and displacement in it is known.
Answer
Work $=$ force $\times $ displacement
$W = F \times S$
Where,
$W =$ work
$F =$ force and
$S =$ displacement
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Question 161 Mark
Write an expression for the kinetic energy of a body of mass m moving with a velocity $v.$
Answer
Mass $= m$
Velocity $= v$
$\text{KE}=\frac{1}{2}\text{mv}^2$
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Question 181 Mark

What happens to the potential energy of a body when its height is doubled?

Answer
The potential energy is doubled when the height is doubled since potential energy is directly proportional to height, h to which body is raised.
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Question 191 Mark

Define the term 'energy' of a body. What is the SI unit of energy.

Answer
Energy: Energy is the ability to do work. SI unit of energy is Joule.
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Question 201 Mark
In which of the following case the work done by a force will be maximum: when the angle between the direction of force and direction of motion is $0^\circ$ or $90^\circ ?$
Answer
Work done will be maximum when angle between the direction of force and direction of motion is 0° because, $\text{W} =\text{F}\cos\theta\times\text{s}.$ And, $\cos\theta\ 0^\circ=1$ and $90^\circ=0$
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Question 231 Mark
What is the condition for a force to do work on a body?
Answer
The condition for a force to do work on a body is that it should produce motion in the body.
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Question 241 Mark
Define $1$ joule of work.
Answer
1 joule: When a force of $1$ newton moves a body through a distance of $1$ meter in its own direction, then the work done is known as $1$ joule.
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Question 251 Mark

Which would have a greater effect on the kinetic energy of an object: doubling the mass or doubling the velocity?

Answer
Doubling the velocity would have a greater effect on kinetic energy.
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Question 261 Mark
What is the kinetic energy of an object?
Answer
Kinetic energy is the energy possessed by a body by the virtue of its motion. Every moving object possesses kinetic energy. A body uses kinetic energy to do work. Kinetic energy of hammer is used in driving a nail into a log of wood, kinetic energy of air is used to run wind mills, etc.
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Question 291 Mark
Relate watt to joule.
Answer
As we know that $\text{Power}=\frac{\text{Work}}{\text{Time}}$ $\text{watt}=\frac{\text{joule}}{\text{second}}$ So if the time is taken as unity then we can define watt in terms of joule. Therefore, One watt power is equal to one joule work when the time taken is unity.
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Question 311 Mark
Which will have more impact on kinetic energy-doubling mass or velocity?
Answer
As kinetic energy of an object is directly proportional to its mass, so if mass is doubled (i.e. it becomes 2m), then kinetic energy will also get doubled. Hence, it is clear that doubling the velocity has a greater effect on the kinetic energy of an object.
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Question 321 Mark
A cell converts one form of energy into another form. Name the two forms.
Answer
A cell converts chemical energy into electrical energy.
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Question 331 Mark

What kind of energy is possessedby the following?

Water stored in the reservoir of a dam.

Answer
Potential energy.
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Question 341 Mark
Write the energy transformations which take place in an electric bulb (or electric lamp).
Answer
In an electric bulb, electrical energy is first converted into heat energy and then into light energy.
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Question 351 Mark
Name the device or machines which convert: Chemical energy into kinetic energy (or mechanical energy).
Answer
Car engine.
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Question 361 Mark
Define the term ‘watt’.
Answer
Watt is the power of an appliance which does work at the rate of 1 joule per second.
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Question 381 Mark
When a ball is thrown vertically upwards, its velocity goes on decreasing. What happens to its potential energy as its velocity becomes zero?
Answer
Potential energy becomes maximum.
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Question 391 Mark
Name the device or machines which convert: Mechanical energy into electrical energy.
Answer
Electric generator.
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MCQ 401 Mark
Energy conservation law says that:
  • A
    Energy can't be destroyed but can be produced.
  • ✓
    Neither energy can be produced nor can be destroyed.
  • C
    Energy can't be produced but can be destroyed.
  • D
    Energy can be produced and can be destoyed
Answer
Correct option: B.
Neither energy can be produced nor can be destroyed.
In physics, the law of conservation of energy states that the total energy of an isolated system remains constant — it is said to be conserved over time. Energy can neither be created nor destroyed; rather, it transforms from one form to another.
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Question 411 Mark
Name the commercial unit of measurement of energy.
Answer
The commercial unit of energy is kilowatt-hour.
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Question 431 Mark
When do we say that work is done?
Answer
Work is done whenever the given conditions are satisfied:
  1. A force acts on the body.
  2. There is a displacement of the body caused by the applied force along the direction of the applied force.
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Question 441 Mark
How much work is done by the gravitational force of earth acting on a satellite moving around it in a circular path? Give reason for your answer.
Answer
The work done is zero because the gravitational force acts along the radius of the circular path, at right angles i.e. $90^\circ$ to the motion of satelite.
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Question 451 Mark
A load of $100\ kg$ is pulled up by $5\ m$. Calculate the work done.$ (8 = 9.8m/s)$
Answer
Mass $= 100\ kg$ Height $= 5\ m\ g = 9.8\ m/s^2$
$P.E. = m \times g \times h = 100 \times 5 \times 9.8 = 4900\ J$
Work done is equal to $PE$ acquired by the body.
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Question 471 Mark
Describe the energy changes which take place in a radio.
Answer
A radio first converts electrical energy into kinetic energy and then into sound energy.
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Question 481 Mark
Define $1J$ of work.
Answer
$1J$ is the amount of work done by a force of $1N$ on an object that displaces it through a distance of $1m$ in the direction of the applied force.
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Question 491 Mark
Is potential energy a vector or a scalar quantity?
Answer
Potential energy is a scalar quantity as it has magnitude only and it does not require any specification of direction.
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Question 501 Mark
Write an expression for the kinetic energy of an object.
Answer
If a body of mass m is moving with velocity v, then its kinetic energy $E_k$ is given by the expression,
$\text{E}_\text{k}=\frac{1}{2}\text{mv}^2$
Its $S.I.$ unit is Joule $(J).$
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