- A75%
- B50%
- C100%
- D66.7%
Work done against gravity = mgh = 20 kg * 10 m/s² * 1.5 m = 300 J. If the person's output work (lifting the suitcase) is 300 J and the energy input as 'work done by the person' is stated as 300 J, then efficiency would be (Output Work / Input Work) * 100% = (300 J / 300 J) * 100% = 100%. This is an ideal scenario for the 'person as a machine' calculation, implying no internal losses for the output work itself.
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?
→ 26Which of the following statements best describes the law of conservation of energy?
→ 27Explain the difference between work and power. Give their SI units.
→ 28In a single movable pulley system, if the load is 400 N, what is the ideal effort required to lift it?
→ 29A 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)
→ 30Why does a long handle make it easier to turn a screw or a wrench?
→ 31A 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?
→ 32If 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.
→ 33Compare the function of an inclined plane with that of a wedge. How are they similar and different in their application?
→ 34A 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?
→ 35A bicycle wheel acts as an example of which simple machine?
→ 36Assertion: 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.
→ 37Why is lubrication used in simple machines?
→ 38A 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:
→ 39Which of the following statements about power is correct?
→ 40A 60 W light bulb operates for 5 hours. How much energy does it consume in joules?
→ 41Explain the energy transformations that occur when a hydroelectric power plant generates electricity.
→ 42If 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?
→ 43A 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.
→ 44A 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?
→ 45Why is a block and tackle system with five pulleys more advantageous than a single movable pulley?
→ 46A 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.
→ 47An 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?
→ 48Which of the following is NOT an example of a Class I lever?
→ 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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