Test: Conservation Of Energy And Power

# Test: Conservation Of Energy And Power - Class 9

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## 10 Questions MCQ Test Science Class 9 - Test: Conservation Of Energy And Power

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Test: Conservation Of Energy And Power - Question 1

### What is the commercial unit of energy?

Detailed Solution for Test: Conservation Of Energy And Power - Question 1

The commercial unit of energy is a kilowatt hour.
One kilowatt hour is defined as the amount of electrical energy consumed when an electrical appliance having a power rating of 1 kilowatt is used for 1 hour.

Test: Conservation Of Energy And Power - Question 2

### A stone weighing 1 kg is dropped from rest from a height of 4 metres above the ground. When it has free-fallen 1 metre its total energy with respect to the ground is

Detailed Solution for Test: Conservation Of Energy And Power - Question 2

Energy is conserved in Free - fall situations ( no external forces doing work). Thus, the total energy would be the same at every stage in failing. Whatever total energy body has initially, it will maintain it throughout the course of its motion.
PE = mgh = 1 x 10 x 4 = 40 J
The object begins with 40 J of potential energy and no Kinetic energy. The total mechanical energy (KE + PE) is 40J.

Test: Conservation Of Energy And Power - Question 3

### A lamp consumes 1000 J of electrical energy in 10 seconds. What is its power?

Detailed Solution for Test: Conservation Of Energy And Power - Question 3

Electrical energy consumed by lamp, W = 1000 J
Time taken, t = 10 seconds Test: Conservation Of Energy And Power - Question 4

When we throw a rock from the top of a building which equation describes the energy of the body at each point during the fall?

Detailed Solution for Test: Conservation Of Energy And Power - Question 4

According to the law of conservation of energy , energy can only be transformed from to form to another , it can neither be created nor destroyed . The total energy before and after the transformation always remains constant.

Test: Conservation Of Energy And Power - Question 5

What is not true about energy?

Detailed Solution for Test: Conservation Of Energy And Power - Question 5
Explanation:
Energy can be created:
- This statement is not true. According to the law of conservation of energy, energy cannot be created or destroyed, but it can only be transformed from one form to another. This principle is known as the first law of thermodynamics.
Energy can move from one object to another:
- This statement is true. Energy can be transferred or transferred from one object to another. For example, when a ball is thrown, the kinetic energy of the person throwing the ball is transferred to the ball, causing it to move.
Energy can be stored:
- This statement is true. Energy can be stored in various forms. For example, potential energy is stored energy that an object possesses due to its position or condition. Chemical energy can be stored in batteries or fuel.
Energy can be transformed from one type of energy to another type of energy:
- This statement is true. Energy can be transformed or converted from one form to another. For example, when a toaster converts electrical energy into heat energy to toast bread, or when a solar panel converts light energy into electrical energy.
In summary, the statement "Energy can be created" is not true. Energy cannot be created or destroyed, but it can be transferred, stored, and transformed from one form to another.
Test: Conservation Of Energy And Power - Question 6

If work is done at a faster rate, then

Detailed Solution for Test: Conservation Of Energy And Power - Question 6
Explanation:
When work is done at a faster rate, the power is increased. This can be understood through the following points:
Definition of Power:
- Power is defined as the rate at which work is done or the amount of work done per unit of time.
- Mathematically, power is calculated as P = W/t, where P is power, W is work, and t is time.
Relationship between Power and Work:
- Power is directly proportional to work.
- When work is done at a faster rate (i.e., completing the same amount of work in less time), the power increases.
- Conversely, if work is done at a slower rate (i.e., completing the same amount of work in more time), the power decreases.
Implications:
- If work is done at a faster rate, it means that more power is being exerted.
- This could be achieved by either applying a greater force or by completing the work in less time.
Therefore, the correct answer is option A: power is more.
Test: Conservation Of Energy And Power - Question 7

A diesel engine supplies 25,000 J of energy in 50 seconds. Power of engine would be

Detailed Solution for Test: Conservation Of Energy And Power - Question 7

Power = Work done / Time
= 25000 / 50
= 500J/s or 500W

Test: Conservation Of Energy And Power - Question 8

If a light bulb is switched on for 20 s and it consumes 2400 J of electrical energy then it's power is

Detailed Solution for Test: Conservation Of Energy And Power - Question 8

Power = Energy /Time

Power = 2400/20

Power = 120w

Test: Conservation Of Energy And Power - Question 9

A ball is thrown vertically upwards. Its velocity keeps on decreasing. What happens to its kinetic energy when its reaches the maximum height?

Detailed Solution for Test: Conservation Of Energy And Power - Question 9

When a body is thrown vertically upward its velocity continuously decreases, kinetic energy also decreases and potential energy increases due to increase in height.

Test: Conservation Of Energy And Power - Question 10

In winters, rubbing of hands together for some time, causes a sensation of warmth mainly because of

Detailed Solution for Test: Conservation Of Energy And Power - Question 10

If you rub your hands together for several seconds, you'll notice that your hands feel warm. That warmth is caused by a force called friction. When objects like your hands come in contact and move against each other, they produce friction. Friction happens when you overcome the resistance of one object rubbing against the other. The force of the friction is opposes the direction of the motion. If you just put your hands together, there's no resistance, so there's no friction produced. Rub them together and there's friction.

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## Science Class 9

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