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Science One word answer.

Work and Energy · Gujarat Board (GSEB) STD 9 (GSEB - English Medium). 53 questions.

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Question 11 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 21 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 71 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 81 Mark
What kind of energy transformations takes place at a hydroelectric power station?
Answer
At a hydroelectric power station, the potential energy of water is transformed into kinetic energy and then into electrical energy.
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Question 91 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 101 Mark
What is the common name of '1kWh' of electrical energy’?
Answer
1kW-h of electrical energy is commonly known as unit of electricity.
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Question 141 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 151 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 181 Mark

A load of 100kg is pulled up by 5m. Calculate the work done. (8 = 9.8m/s)

Answer
Mass = 100kg
Height = 5m
g = 9.8m/s2
P.E. = m × g × h
= 100 × 5 × 9.8 = 4900J
Work done is equal to PE acquired by the body.
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Question 191 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 201 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 211 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 221 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 241 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° or 90°?
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 251 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 261 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 281 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 291 Mark
Name the device or machines which convert:
Mechanical energy into electrical energy.
Answer
Electric generator.
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Question 301 Mark
Name the commercial unit of measurement of energy.
Answer
The commercial unit of energy is kilowatt-hour.
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Question 311 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 321 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 331 Mark
Name the device or machines which convert:
Heat energy into kinetic energy (or mechanical energy).
Answer
Steam engine.
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Question 341 Mark
Name the device or machines which convert:
Chemical energy into kinetic energy (or mechanical energy).
Answer
Car engine.
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Question 351 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, v2.
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Question 361 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 381 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 391 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 411 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 421 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 431 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 471 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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