- AEnergy can be created or destroyed, but only in nuclear reactions.
- BThe total amount of energy in an isolated system remains constant, though it may change forms.
- CEnergy is always lost as heat in any process.
- DPotential energy is always converted to kinetic energy.
The law of conservation of energy states that energy cannot be created or destroyed, but it can be transformed from one form to another. In an isolated system, the total amount of energy remains constant.
More Questions on Work, Energy, and Simple Machines
1A student performs an experiment with a lever. She applies an effort of 20 N and lifts a load of 60 N. If the effort arm is 30 cm, what is the length of the load arm?
→ 2Looks good. I have 50 questions now. I will carefully format the HTML.A person pushes a rigid wall with a force of 200 N for 10 seconds but the wall does not move. What is the work done by the person on the wall?
→ 3Consider the energy transformation in a person pushing a heavy box across a rough floor. Identify the primary forms of energy involved and how they change.
→ 4Let's make a new question instead of fixing this one, as fixing it would involve changing the question itself, which is against the rules. New Q50: A student performs an experiment with a lever. She applies an effort of 20 N and lifts a load of 60 N. If the effort arm is 30 cm, what is the length of the load arm?
→ 5A person uses an inclined plane to push a heavy box to a height of 3 m. The length of the inclined plane is 5 m. If the force required to push the box up the incline is 100 N, and the weight of the box is 300 N, calculate the efficiency of the inclined plane.
→ 6Two workers, A and B, lift identical boxes to the same height. Worker A takes 2 minutes, while worker B takes 1 minute. Which worker has more power?
→ 7Why is the efficiency of a real machine always less than its ideal mechanical advantage divided by its velocity ratio?
→ 8A diver jumps from a diving board. Describe the energy transformations involved from the moment she leaves the board until she hits the water.
→ 9A lever used to open a bottle cap is an example of which class of lever?
→ 10Assertion: A force acting on an object does no work if the object does not move. Reason: Work done is defined as the product of force and displacement.
→ 11Can an object possess energy without possessing momentum? Justify your answer.
→ 12In the context of work, why is it said that "force does work"?
→ 13A 100 W bulb is left on for 10 hours. If electricity costs Rs. 5 per unit (1 unit = 1 kWh), what is the cost of using the bulb?
→ 14How does increasing the number of pulleys in a block and tackle system affect its mechanical advantage and the distance the effort needs to move?
→ 15A person pushes a shopping cart with a force of 50 N at an angle of 30 degrees below the horizontal. If the cart moves 10 m, what is the work done by the person on the cart? (cos 30° = 0.866)
→ 16Why is a screw considered a type of inclined plane?
→ 17An object of mass 2 kg falls from a height of 10 m. What is its potential energy at half the height? (Take g = 10 m/s²)
→ 18Give two everyday examples for each of the three classes of levers.
→ 19A machine has an efficiency of 75%. If the input energy is 400 J, how much useful work is done by the machine?
→ 20What is the condition for work done to be positive?
→ 21A spring is compressed by a distance 'x'. If the compression is doubled to '2x', how does the elastic potential energy stored in the spring change?
→ 22Discuss the advantages of using a single movable pulley versus a single fixed pulley.
→ 23If a human heart pumps 70 mL of blood in one beat against a pressure of 120 mmHg (equivalent to 16000 Pa) and beats 72 times per minute, calculate the power of the heart. (1 mL = 10^-6 m³)
→ 24An object is moving with constant velocity on a rough horizontal surface. What is the net work done on the object?
→ 25A loaded truck requires less effort to push up a longer, less steep ramp than a shorter, steeper ramp to reach the same height. Which simple machine principle is at play here?
→ 26Explain the difference between work and power. Give their SI units.
→ 27In a single movable pulley system, if the load is 400 N, what is the ideal effort required to lift it?
→ 28A motor raises a 500 kg load through a vertical height of 10 m in 20 seconds. Calculate the power of the motor. (Take g = 10 m/s²)
→ 29Why does a long handle make it easier to turn a screw or a wrench?
→ 30A boy running at 4 m/s has a kinetic energy of 40 J. If he doubles his speed, what will be his new kinetic energy?
→ 31If a 100 N force is applied to move a box 5 m horizontally, but the angle between the force and displacement is 60 degrees, calculate the work done.
→ 32Compare the function of an inclined plane with that of a wedge. How are they similar and different in their application?
→ 33A mass of 5 kg is accelerated uniformly from rest to 10 m/s in 2 seconds. What is the kinetic energy of the mass after 2 seconds?
→ 34A bicycle wheel acts as an example of which simple machine?
→ 35Assertion: The work done by a force can be zero even if the force and displacement are non-zero. Reason: Work done is a scalar quantity and depends on the angle between force and displacement.
→ 36Why is lubrication used in simple machines?
→ 37A man carries a load of 20 kg on his head and walks 100 m on a horizontal road. The work done by the man against gravity is:
→ 38Which of the following statements about power is correct?
→ 39A 60 W light bulb operates for 5 hours. How much energy does it consume in joules?
→ 40Explain the energy transformations that occur when a hydroelectric power plant generates electricity.
→ 41If a force F acts on an object at an angle theta to the direction of displacement d, the work done is given by W = Fd cos(theta). Under what condition will the work done be zero?
→ 42A person climbs a hill, while another person of the same mass takes an elevator to the same height. Compare the work done by gravity on both persons.
→ 43A 2 kg mass is attached to a spring with a spring constant k. It is pulled by 0.1 m and released. What type of energy is stored in the spring when it is pulled?
→ 44Why is a block and tackle system with five pulleys more advantageous than a single movable pulley?
→ 45A machine lifts a load of 1000 N by applying an effort of 250 N. If the load is raised by 2 m and the effort applied moves 10 m, calculate the efficiency of the machine.
→ 46An object of mass 'm' is dropped from a height 'H'. What is its total mechanical energy just before it hits the ground, assuming no air resistance?
→ 47Which of the following is NOT an example of a Class I lever?
→ 48A person lifts a 20 kg suitcase to a height of 1.5 m. The work done by the person is 300 J. What is the efficiency of the person as a 'lifting machine' if we consider their energy expenditure?
→ 49Explain why a machine can never have 100% efficiency.
→ 50Two identical cars, A and B, are moving such that car A has twice the speed of car B. What is the ratio of their kinetic energies (KE_A : KE_B)?
→ 51A pendulum bob oscillates. At which point in its swing is its kinetic energy maximum and potential energy minimum?
→ 52Which type of lever always has a mechanical advantage greater than 1?
→ 53A worker pulls a block along a horizontal surface with a constant force of 50 N, covering a distance of 10 m. If the force of friction acting on the block is 10 N, what is the net work done on the block?
→ 54Distinguish between ideal mechanical advantage (IMA) and actual mechanical advantage (AMA) of a simple machine.
→ 55A stone is dropped from a height 'h'. If its speed just before hitting the ground is 'v', what is the stone's kinetic energy at the moment it is dropped?
→ 56Which of the following activities involves negative work done by a force?
→ 57A boy of mass 40 kg climbs a flight of 50 stairs, each 15 cm high, in 25 seconds. Calculate the power exerted by the boy. (Take g = 10 m/s²)
→ 58Why is a single fixed pulley considered to have a mechanical advantage of 1?
→ 59A 10 kg object is lifted to a height of 5 meters. Calculate the work done against gravity. (Take g = 10 m/s²)
→ 60A machine has a mechanical advantage of 4 and a velocity ratio of 5. What is the efficiency of the machine?
→ 61A ball is thrown vertically upwards. What happens to its kinetic energy and potential energy as it rises to its maximum height?
→ 62A person pushes a rigid wall with a force of 200 N for 10 seconds but the wall does not move. What is the work done by the person on the wall?
→ 63What are the various energy transformations that occur when you are riding a bicycle?
→ 64The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
→ 65A 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.
→ 66Certain force acting on a 20 kg mass changes its velocity from 5 m/s to 2 m/s. Calculate the work done by the force.
→ 67A battery lights a bulb. Describe the energy changes involved in the process
→ 68An object is thrown at an angle to the ground. It moves in a curved path and falls back to the ground. The starting and ending points are at the same height. What is the work done by gravity on the object?
→ 69A lamp consumes 1000 J of electrical energy in 10 s. What is its power?
→ 70Define 1 watt of power.
→ 71What is power?
→ 72The kinetic energy of an object of mass m moving with a velocity of 5 m/s is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?
→ 73Write an expression for the kinetic energy of an object.
→ 74What is the kinetic energy of an object?
→ 75A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?
→ 76Define 1 J of work.
→ 77Write an expression for the work done when a force is acting on an object in the direction of its displacement.
→ 78When do we say that work is done?
→ 79A force of 7 N acts on an object. The displacement of the object is 8 m in the direction of the force. What is the work done by the force?
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