Chapter-11 Work and Energy

1. When do we declare a task complete?

Explanation:

When the predetermined requirements are met, the work is finished:

(i) The body is subject to a force.

(ii) When force is applied in the force's direction or in the opposite direction, the body is displaced.


2. An object is subject to a 7 N force. The displacement is, let's say, 8 m in the force's direction. Let's assume that the displacement is how the force affects the item. What is the task at hand in this instance?

Explanation:

Work is accomplished when a force F moves an object through a distance S in its direction.

Force is used to perform the task on the body.

Force plus displacement equals work done.

W = F × S

Where,

F = 7 N S = 8 m

Work completed,

W = 7 × 8

W = 56 Nm

W = 56 J h


3.Create an expression to describe the work done when a force is applied to an object that is moving in the direction of the force.

Explanation:

The work done W on the body is provided by the statement when a force F displaces it via a distance S in the direction of the applied force:

W = F × S


4. The force applied to a plough by two bullocks is 140 N. A 15-meter-long field is being ploughed.How labor-intensive is it to plough a field from end to end

Explanation:

The following expression indicates the work performed by bullocks:

W= F × d

Where,

F = 140 N is the applied force.

Movement, d = 15 m

W = 140 x 15 = 2100 J

Plowing the length of the field therefore requires 2100 J of labour.


5.  What is an object's kinetic energy?

Explanation:   

Mechanical energy or kinetic energy is the energy a body possesses as a result of its motion. Every thing in motion has mechanical energy. A body attempts to function by using mechanical energy. The mechanical energy of air is used to spin wind turbines, the kinetic energy of the hammer is used to drive a nail into a log of wood, etc.


6. Specify one J of work.

 Explanation: 

When an object is moved by 1 m along the force's line of action by a force of 1 N, the amount of work done on the object is 1 J.


7. What exactly is power?

Explanation:

Power is characterised as the speed at which work is completed or energy is transferred. Power is given by: If an agent completes a task W in time t, then

P = W/T

It is measured in watts (W)


 8.  A mass of m moving at a speed of 5 m/s has a kinetic energy of 25 J. When its velocity doubles, what will its kinetic energy be? When its velocity is tripled, what will be its kinetic energy?

Explanation: 

A mass of m moving at a speed of 5 m/s has a kinetic energy of 25 J. When its velocity doubles, what will its kinetic energy be? When its velocity is tripled, what will be its kinetic energy?

Explanation:

Given

The object's K.E. is 25J.

The object's speed (v) is 5 m/s.

K.E. = (½) mv2

25 = (½) m (5)2

50 = 25 x m

m = 50/25

m = 2 kg

When velocity doubles now

v = 10 m/s

m = 2 kg

K.E. = (½) x 2 x (10)2

K.E. = 102

K.E. = 100 J

Increasing velocity three times results in

v = 15 m/s

m = 2 kg

K.E. = (½) x 2 x (15)2

K.E. = (15)2

K.E. = 225 J


9. What exactly is power?

Explanation:

Power is characterised as the speed at which work is completed or energy is transferred. Power is given by: If an agent completes a task W in time t, then

P = W/T

  It is measured in watts (W)


10. A lamp uses 1000 J of electricity in just 10 seconds. What is its strength?

Explanation:

Power = Time/Work

P = W/T

Time = 10 s

Work completed equals 1000 J of energy used by the bulb.

1000/10 = 100 Js-1 = 100 W

Hence, the lamp's power is 100 W



11. Describe average power.

Explanation:

The ratio of the body's total labour to its whole time spent is known as average power.


12. The potential energy of a freely falling object gradually decreases. Does this violate the rule governing energy conservation? Why?

Explanation:

The strategy does not violate the principle of energy conservation. This is because during a fall from a height, the body's potential energy gradually transforms into kinetic energy. When the system's potential energy falls, the body's kinetic energy rises. The complete mechanical energy of the organism is maintained throughout. As a result, the law of conservation of energy is not broken.


13. What different energy conversions take place when you ride a bicycle?

Explanation:

The rider's muscle energy is converted into heat and mechanical energy while pedalling a bicycle. The bicycle's kinetic energy gives it motion, while thermal energy warms our bodies.

Heat + mechanical energy =muscular energy 


14. On a table, a mass of 10 kg is located at point A. It is transferred to point B. What does the gravitational force do to an object if the line connecting A and B is horizontal? Describe your response.

Explanation:

The only factor affecting the work that gravity does is the body's vertical displacement. It is independent of the body's track. Thus, the expression, gives the amount of work done by gravity.

W= m g h

Where,

h = 0 vertical displacement

W = M + G + 0 = 0

Gravity therefore does not exert any force on the thing.


15. Does energy transfer occur when you push a large rock with all of your strength and it doesn't budge? Where does the effort you put forth go?

Explanation:

No muscular energy is transferred to the stationary rock when we push a heavy object. Also, there is no energy waste because the muscle energy that drives our body's production of heat is converted into heat energy.


16. Over the course of a month, a particular household used 250 units of energy. In joules, how much energy is this?

Explanation:

1 kWh is one unit of energy.

Given

250 units equal 1 energy (E).

kWh = 1 unit.

1 kWh = 3.6 x 106 J

Hence, 250 units of energy are equal to 250 3.6 106.= 9 × 108 J.


17.  What does the force of gravity on a satellite orbiting the earth accomplish? Explain your response.

Explanation:

When the first two requirements are met, work is finished:

(i) The body is subject to a force.

(ii) When force is applied in the force's direction or in the opposite direction, the body is displaced.

(iii) The work done is 0 if the force's direction is perpendicular to the displacement. 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 satellite.


18. A 40 kg object is raised to a 5 m height above the ground. What is the amount of potential energy? Find the object's kinetic energy halfway down if it is allowed to fall.

Explanation:

If Mass (m) = 40 kg, then

Gravitational acceleration (g) equals 10 m/s2.

Height (h) = 5m

Energy potential = m g h

P.E= 40 × 10 × 5 = 2000J

Energy potential = 2000J ( 2000 joules)

The object has a potential energy of 2000 J at a height of 5 metres.

Half of 5 metres, or 5/2, or 2.5 metres, will be this object's height above the earth when it is permitted to fall and halfway down.

PE at the halfway point = m g h

P.E= 40× 10 × 2.5= 1000J

[h= 2.5 m]



19.  Can an object move when no force is applying pressure to it? Think. Your buddies and teacher should discuss this.

Explanation:

Without any external forces acting on it, an object can indeed move. The result of a single force acting on an object is acceleration. A force is acting on something if it accelerates.

Make the assumption that an object is travelling at a constant speed. It is being pulled by nothing at all. Although the thing is moving, there is also a displacement. Therefore, even in the absence of a force, there can still be displacement.


20. After 30 minutes of holding a hay bundle over his head, a person becomes fatigued. Has he completed any work? Explain your response.

Explanation:

When one of the first two requirements is met, work is finished.

(i) The body is subject to a force.

(ii) When force is applied in the force's direction or in the opposite direction, the body is displaced.

There is no displacement in the hay bundle when a person holds it over his head. Despite the fact that the bundle is being pulled downward by gravity, no force is being applied to it by the individual. As a result, the person's work on the bundle is zero in the absence of force.


21. After 30 minutes of holding a hay bundle over his head, a person becomes fatigued. Has he completed any work? Explain your response.

Explanation:

When one of the first two requirements is met, work is finished.

(i) The body is subject to a force.

(ii) When force is applied in the force's direction or in the opposite direction, the body is displaced.

There is no displacement in the hay bundle when a person holds it over his head. Despite the fact that the bundle is being pulled downward by gravity, no force is being applied to it by the individual. As a result, the person's work on the bundle is zero in the absence of force.


22. A mass m object is travelling at constant speed v. How much labour must be put into the object in order to put it to rest?

Explanation:

The formula, gives the kinetic energy of a mass m object travelling at a velocity v.

K.E = 1/2 mv^2

Its velocity must be decreased to zero in order to bring it to rest, and in order to do that, the kinetic energy must be removed and transmitted somewhere else.An outside force must either provide negative work on an object equal to its kinetic energy, or it must take energy from the object.


23. A mass m object is travelling at constant speed v. How much labour must be put into the object in order to put it to rest?

Explanation:

The formula, gives the kinetic energy of a mass m object travelling at a velocity v.

K.E = 1/2 mv^2


24. A 1500 W electric heater is available. Throughout ten hours, how much energy does it consume?

Explanation:

Given,

The heater has a power of 1500 W, or 1.5 kW.

That took 10 hours.

An electric heater's energy consumption can be calculated using the phrase,

Power is calculated as Energy / Time.

Hence,

Energy used equals Power times Time.

Energy used equals 1.5 x 10.

Consumed energy is 15 kWh.

Hence, the heater uses 15 kWh of electricity in 10 hours.


25. Use the energy changes that take place when we draw a pendulum bob to one side and allow it to oscillate as an example of the law of conservation of energy. Why ultimately does the bob stop? What ultimately happens to its energy? Is it a contravention of the law of energy conservation?

Explanation:

Think about an oscillating pendulum as an example.

An apparatus rises via a height h on top of the mean level P when it moves from its mean position P to either of its extreme locations A or B. The bob's K.E. now completely transforms into P.E. The K.E. drops to zero, and the bob also has P.E.


26.  According to laya , an object's acceleration may be zero even if other forces are at work. Are you in accord with her? Why?

Explanation:

Other of forces 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 object that is travelling uniformly is zero. As a result, there is no acceleration of the object. Laya is therefore correct.


27. When an object is falling freely, it eventually comes to rest on the ground. How is its kinetic energy transformed?

Explanation:

Restential energy diminishes and kinetic energy grows when an object descends freely towards the earth; once the object strikes the ground, all of its potential energy is converted to kinetic energy. All of the object's kinetic energy transforms into heat and sound energy as it strikes the earth. Depending on the type of ground and the object's kinetic energy, it can also cause the ground to deform.


28. Calculate the amount of energy (in kW/h) used by four 500 W-powered devices in 10 hours.

Explanation:

Given,

The device's power rating (P) is 500 W, or 0.50 kW.

The device runs for 10 hours (T).

The formula can be used to calculate the amount of energy used by an electric device.

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 devices of similar rating in 10 hours will be

⇒ 4 × 5 kWh

= 20 kWh


29. Create a formula to describe an object's kinetic energy.

Explanation:

Assume a body with mass m is travelling at velocity v. As a result, its kinetic energy Ek is determined by:

Ek=12mv2


30.  What is average power?

Explanation:

The ratio of the body's total labour to its whole time spent is known as average power.

·       The average power equal to total work by total time.