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Science Question Answer (1 Marks)

Work and Energy · Maharashtra Board STD 9 (MSBSHSE - Semi English Medium). 106 questions.

Questions · Page 2 of 3

Question Answer (1 Marks)

Question 511 Mark
What should be the angle between the direction of force and the direction of motion of a body so that the work done is zero?
Answer
The work done will zero when angle between the direction of force and direction of motion is 90° because,
$\text{W} =\text{F}\cos\theta\times\text{s}.$
And $\cos\theta\ 90^\circ=0$
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Question 521 Mark
Define kilowatt-hour.
Answer
One kilowatt-hour is the amount of electrical energy consumed when an electrical appliance having power of 1 kilowatt is used for 1 hour.
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Question 541 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 631 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 651 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 671 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 681 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 691 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 $0^\circ$ 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 721 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 731 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 741 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 781 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 791 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 801 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 811 Mark
Name the device or machines which convert:
Chemical energy into kinetic energy (or mechanical energy).
Answer
Car engine.
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Question 821 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 841 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 851 Mark
Name the device or machines which convert:
Mechanical energy into electrical energy.
Answer
Electric generator.
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Question 861 Mark
Name the commercial unit of measurement of energy.
Answer
The commercial unit of energy is kilowatt-hour.
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Question 881 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° to the motion of satelite.
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Question 891 Mark
A load of $100\ kg$ is pulled up by $5\ m.$ Calculate the work done. $(8 = 9.8\ m/s)$
Answer
Mass $= 100\ kg$
Height $= 5\ m$
g $= 9.8\ m/s^2$
P.E. $= m \times g \times h$
$= 100 \times 5 \times 9.8 = 4900J$
Work done is equal to PE acquired by the body.
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Question 911 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 921 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 931 Mark
Name two units of power bigger than watt.
Answer
Megawatt and kilowatt are the units of power bigger than watt.
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Question 941 Mark
A body is thrown vertically upwards. Its velocity goes on decreasing. What happens to its kinetic energy as its velocity becomes zero?
Answer
When the velocity becomes zero, the kinetic energy also becomes zero since kinetic energy is directly proportional to square of the velocity.
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Question 951 Mark
Name the device or machines which convert:
Heat energy into kinetic energy (or mechanical energy).
Answer
Steam engine.
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Question 961 Mark
How much work is done when a force of 1N moves a body through a distance of 1m in its own direction?
Answer
Force, F = 1N
Distance, s = 1m
Work done W = F × s
= 1 × 1 = 1J
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Question 971 Mark
A body does 1200 joules of work in 2 minutes. Calculate its power.
Answer
Work done = 1200J
Time taken 2 minutes
= 2 × 60 = 120s
$\text{Power}=\frac{\text{Work done}}{\text{Time taken}}=\frac{1200}{120}=10\text{W}$
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Question 981 Mark
What do you understand by the kinetic energy of a body?
Answer
kinetic energy: The energy of a body due to its motion is called kinetic energy.
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Question 1001 Mark
On what factors does the kinetic energy of a body depend?
Answer
The kinetic energy of a body depends on:
  1. Mass of the body, m.
  2. Square of the velocity of the body, $v^{2.}$
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Question Answer (1 Marks) - Page 2 - Science STD 9 Questions - Vidyadip