1. Look at the activities listed below. Reason
Out whether or not work is done in the light of your understanding of the term ‘work’.
Suma is swimming in a pond.
Donkey is carrying a load on its back.
A wind-mill is lifting water from a well.
A green plant is carrying out photosynthesis.
An engine is pulling a train.
Food grains are getting dried in the sun.
A sailboat is moving due to wind energy.
1. Look at the activities listed below. Reason
Out whether or not work is done in the light of your understanding of the term ‘work’.
Suma is swimming in a pond.
Donkey is carrying a load on its back.
A wind-mill is lifting water from a well.
A green plant is carrying out photosynthesis.
An engine is pulling a train.
Food grains are getting dried in the sun.
A sailboat is moving due to wind energy.
Explanation:
Anytime either of the following two criteria is met, the work is complete:
The organism is subject to a stimulus.
When force is applied in the force's direction or in the opposing direction, the entity is displaced.
Suma uses power while swimming to compel the water to move backward. As a result, Suma swims in a forward trajectory as a result of the water's forward response. The impact here results in a shift. Therefore, Seema completes the task while swimming.
The donkey needs to exert an upward motion while bearing a load. However, the weight is being displaced in a forward path. The labour done is nil because displacement is perpendicular to force.
Water is raised by a turbine by working against gravity. Water is lifted by a turbine by exerting an upward force, and as a result, the water is also flowing upward. As a result, the turbine works to raise water from the well.
When a verdant plant is performing photosynthesis, no power is necessary. The plant doesn't shift by applying any effort. Because there is no power or movement. So, nothing is accomplished.
When a railway is being pulled by an engine, that engine is exerting energy forward. As a result, it is going forward. Because power and displacement both move in the same way. As a result, the motor works.
Food grains are dried in the sun without any power being applied, and the grains do not move. Since neither a force nor a movement exists. So, nothing is accomplished.
A ship that is propelled forward by wind power is exerting force in that direction. As a result, it is going forward. Because power and displacement both move in the same way. So, the job is finished.
2. An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?
2. An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?
Explanation:
The only factor that influences the work that gravity does on an item is vertical movement. The difference between the object's starting and end positions/heights, which are both zero, determines the vertical displacement. The term, "gravitational work," provides information.
W = m × g × h
Where,
Vertical shift of h = 0
W = m g × 0 = 0 J
As a result, there is no energy expended by gravity on the provided item.
3. A battery lights a bulb. Describe the energy changes involved in the process.
3. A battery lights a bulb. Describe the energy changes involved in the process.
Explanation:
When a battery and a bulb are linked, the battery's energy is converted into electricity. The voltage is converted into light and thermal energy once it reaches the lamp. As a result, the energy change in the scenario can be represented as:
Heat energy, chemical energy, electrical energy, and light energy.
4. Certain force acting on a 20 kg mass changes its velocity from 5 m s-1 to 2 m s-1. Calculate the work done by the force
4. Certain force acting on a 20 kg mass changes its velocity from 5 m s-1 to 2 m s-1. Calculate the work done by the force
Explanation:
Given
Initial speed, u, is 5 m/s.
20 kg is the body's weight.
Final speed is 2 m/s.
The mechanical energy at first
Ei = (1/2) mu2 = (1/2) × 20 × (5)2
= 10 × 25
= 250 J
Mechanical energy at rest
Ef = (1/2) mv2 = (1/2) × 20 × (2)2
= 10 × 4
= 40 J
Therefore,
Change in moving energy equals work done.
Work completed = Ef - Ei.
Work completed equals 40 - 250 J
Work completed: -210 J
5. A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.
5. A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.
Explanation:
The only factor affecting the work that gravity does is the body's vertical movement. It is independent of the body's path. Therefore, the expression, gives the amount of labour done by gravitation.
W= m g h
Where,
h = 0 vertical movement
W equals M + G + 0 = 0
Gravity therefore does not exert any force on the item.
6. The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
6. The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Explanation:
The approach does not go against the rule of energy saving. This is due to the gradual conversion of the body's potential energy into motion energy during a fall from a height. The body's dynamic energy increases when the potential energy of the system decreases. The body's entire kinetic energy is preserved throughout the entire process. The rule of conservation of energy is not violated as a result.
7. What are the various energy transformations that occur when you are riding a bicycle?
7. What are the various energy transformations that occur when you are riding a bicycle?
Explanation:
When someone rides a bicycle, their bodily energy is transformed into the heat and rotational energy of the vehicle. The entire amount of energy is preserved during change. The rider's muscle energy is converted back into mechanical and thermal energy. The bicycle's kinetic energy gives it motion, while thermal energy warms our bodies. Therefore, while pedalling a bicycle, different energy changes take place, converting muscle energy to kinetic and heat energy.
Heat in addition to kinetic energy = muscular energy
8. Does the transfer of energy take place when you push a huge rock with all you might and fail to move it? Where is the energy you spend going?
8. Does the transfer of energy take place when you push a huge rock with all you might and fail to move it? Where is the energy you spend going?
Explanation:
The process by which energy changes its shape is known as an energy shift. While energy can be transformed, energy conservation alludes to the reality that the overall amount of energy remains constant. When we propel a big boulder, there is no muscle energy transfer to the stationary rock. Furthermore, there is no energy waste because our bodies heat up as muscular energy is transformed to thermal energy. The conservation of energy principle has taught us that energy cannot be produced or eliminated; it can only be changed from one state to another.
9. A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
9. A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
Explanation:
1 kWh is one measure of energy.
Given
250 units equal 1 energy (E).
KWh equals 1 unit.
1 kWh equals 3.6 x 106 J
Consequently, 250 units of energy are equal to 250 3.6 106.
= 9 × 108 J.
10. An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
10. An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
Explanation:
: If Mass (m) equals 40 kg, then
Gravitational acceleration (g) equals 10 m/s2.
Height (h) equals 5m
Energy potential equals m g h
P.E= 40 × 10 × 5 = 2000J
Energy potential equals 2000J (2000 joules)
The item has a potential energy of 2000 J at a height of 5 meters.
Half of 5 meters, or 5/2, or 2.5 meters, will be this object's height above the earth when it is permitted to fall and halfway down.
PE at the halfway point equals m g h
P.E= 40× 10 × 2.5= 1000J
[h= 2.5 m]
1000 joules is the potential energy at half-way down.
In accordance with the principle of energy conservation:
Total potential energy is equal to motion energy plus potential energy.
Midway down, 2000 equals 1000 plus K.E.
KE at the midway point equals 2000-1000=1000 J
Kinetic energy midway through is 1000 joules.
11. What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
11. What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Explanation:
When the first two requirements are met, work is finished:
The organism is subject to a stimulus.
When force is applied in the force's direction or in the opposing direction, the entity is displaced.
The labour done is negative if the force's orientation is perpendicular to the shift. The force of gravity acting on a satellite as it orbits the Earth is perpendicular to the spacecraft's motion. As a result, the Earth has done no work at all on the spacecraft.
12. Can there be displacement of an object in the absence of any force acting on it? Think. Discuss this question with your friends and teacher
12. Can there be displacement of an object in the absence of any force acting on it? Think. Discuss this question with your friends and teacher
Explanation:
Yes, even in the lack of external forces operating on an item, displacement may still occur. An object accelerates when only one power works on it. When something moves faster, a force is exerted on it. Assume that something is traveling at a steady speed. It is not under any net influence at all. But the object's velocity is accompanied by a shift. As a result, a shift can occur without a power.
13. A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.
13. A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.
Explanation:
When either of the first two requirements is met, work is finished.
The organism is subject to a stimulus.
By exerting power in the force's direction or in the opposing direction, the body is moved.
There is no movement in the hay bundle when a person lifts it over his head. Despite the fact that the bundle is being pulled downward by gravity, no power is being applied to it by the individual. As a result, the person's labour on the bundle is zero in the lack of force.
14. An electric heater is rated 1500 W. How much energy does it use in 10 hours?
14. An electric heater is rated 1500 W. How much energy does it use in 10 hours?
Explanation:
Given,
The burner has a power of 1500 W, or 1.5 kW.
It took 10 hours.
An electric heater's energy consumption can be calculated using the phrase,
Power is calculated as Energy x Time.
Hence,
Energy used equals Power times Time.
Energy used equals 1.5 times 10.
Consumed energy is 15 kWh.
As a result, the burner used 15 kWh of electricity over the course of 10 hours.
15. Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
15. Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
Explanation:
Think about an oscillating pendulum as an example.
An apparatus raises through a height h on top of the mean level P when it shifts from its mean location P to either of its extreme positions A or B. The bob's K.E. now completely transforms into P.E. The K.E. decreases to zero, and the wave now only has P.E. Its P.E. steadily drops as it gets closer to goal P. As a result, the K.E. will rise. The bob's P.E. becomes zero when it approaches objective P, and it also only has K.E. This technique will always work as long as the device oscillates.
The oscillation doesn't continually move. It requires respite because air pressure prevents it from moving. In an effort to overcome this inertia, the device loses K.E. and occasionally pauses. Because the environment gains energy from the energy wasted by the device to overcome friction, the rule of conservation of energy is not violated. As a result, both the system surrounding the device and its total energy are maintained.
16. An object of mass, m is moving with a constant velocity, v. How much work should be done on the object in order to bring the object to rest?
16. An object of mass, m is moving with a constant velocity, v. How much work should be done on the object in order to bring the object to rest?
Explanation:
The formula, gives the kinetic energy of a mass m object traveling at a rate v.
K.E = 1/2 mv2
Its motion must be decreased to zero in order to put it to rest, and in order to do that, the kinetic energy must be removed and sent somewhere else.
An outside agent must either perform negative work on an object equivalent to its kinetic energy, or it must take energy from the object.
– 1/2 mv2.
17. Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h.
17. Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h.
Explanation:
details provided
The torso weighs 1500 kg.
Speed v = 60 km/h
Change in kinetic energy equals the effort necessary to stop the moving vehicle.
18. In each of the following a force, F is acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.
18. In each of the following a force, F is acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.
Explanation:
Case I
In this instance, the force acting on the object is directed in a direction perpendicular to the shift. As a result, there will be no work done on the block by force.
Case II
The force acting on the object in this instance is acting in the direction of movement. Force applied to the block will therefore result in good effort.
Case III
The force acting on the object in this instance is acting in the opposite direction to the movement. As a result, applying power to the block will result in negative labour.
19. Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
19. Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
Explanation:
A lot of factors may be acting on an item, but it still may not be moving at all. This occurs when all of the forces cancel each other out, leaving zero online forces acting on the item. The online force acting on an item that is moving evenly is zero. As a result, there is no motion of the object. Soni is therefore right.
20. Find the energy in kW h consumed in 10 hours by four devices of power 500 W each.
20. Find the energy in kW h consumed in 10 hours by four devices of power 500 W each.
Explanation:
Given,
The device's power capacity (P) is 500 W, or 0.50 kW.
The gadget operates for 10 hours (T).
The formula can be used to calculate the amount of energy used by and electronic gadget.
Power is equal to energy used/time spent.
Energy used is equal to Power Time.
Energy used equals 0.50 x 10.
Energy used equals 5 kWh.
As a result, the energy used by four gadgets of equivalent rating in 10 hours will be
⇒ 4 × 5 kWh
= 20 kWh
21. A freely falling object eventually stops on reaching the ground. What happens to its kinetic energy?
21. A freely falling object eventually stops on reaching the ground. What happens to its kinetic energy?
Explanation:
Potential energy decreases and kinetic energy rises as an item falls freely toward the earth; once the object hits the ground, all of its potential energy is converted to kinetic energy. All of the object's kinetic energy transforms into heat and aural energy when it strikes the earth. Depending on the type of ground and the object's moving energy, it may also cause the ground to shift.
