Test: Conservation Of Energy And Power - Class 9 MCQ

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.

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.

Electrical energy consumed by lamp, W = 1000 J
Time taken, t = 10 seconds 

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.

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.

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.

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

Power = Energy /Time

Power = 2400/20

Power = 120w

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

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.