Work and Machines
100: What is the scientific definition of work?
Answer: Work is defined as a force applied through a distance.
100: What is kinetic energy?
Answer: Kinetic energy is the energy due to motion, depending on mass and speed.
100: What is the law of conservation of energy?
Answer: Energy cannot be created or destroyed, only converted from one form to another.
100: What are simple machines?
Answer: Simple machines are devices that change the force needed to do work and operate with one movement.
100: How do you calculate kinetic energy?
Answer: KE (joules) = (1/2)mv², where m is mass in kg and v is speed in m/s.
200: Name a machine that changes the direction of force.
Answer: A fixed pulley.
200: What is gravitational potential energy and how is it calculated?
Answer: Gravitational potential energy is energy due to gravitational force; GPE = mass (kg) x gravity (N/kg) x height (m).
200: What is mechanical energy?
Answer: Mechanical energy is the sum of kinetic energy and potential energy in a system.
200: Provide an example of a compound machine.
Answer: A bicycle is a compound machine because it combines several simple machines.
200: What is the formula for calculating power?
Answer: P (watts) = energy (J) / time (seconds)
300: What is the formula for calculating work?
Answer: Work (J) = force (N) x distance (m).
300: Name two types of potential energy.
Answer: Elastic potential energy and chemical potential energy.
300: How does friction affect the mechanical energy of a system?
Answer: Friction converts mechanical energy into thermal energy, reducing the total mechanical energy.
300: What is efficiency in terms of machines?
Answer: Efficiency is the ratio of output work to input work, expressed as a percentage.
300: If a runner's power is 400 W, how much energy does she convert in 10 minutes?
Answer: Energy = Power x Time = 400 W x 600 s = 240,000 J.
400: Explain the concept of mechanical advantage.
Answer: Mechanical advantage is the effectiveness at increasing force; it is the ratio of output force to input force.
400: How does energy transfer occur in a system?
Answer: Energy is transferred by work, causing changes in the system.
400: Explain how power is related to energy.
Answer: Power is the rate at which energy is converted; measured in watts.
400: How do machines make work easier?
Answer: Machines make work easier by changing the force needed to do the work or increasing speed.
400: How much energy can a 150-horsepower engine transform in 10.0 seconds?
Answer: Energy = Power x Time = (150 hp x 746 W/hp) x 10 s = 1,119,000 J.
500: What are the benefits of using machines in everyday tasks?
Answer: Machines increase speed, increase force, and change the direction of force.
500: Describe how the speed of molecules in air relates to their masses.
Answer: On average, molecules with smaller masses will be moving faster.
500: If a roller coaster is at the top of a hill, where is the kinetic energy greater as it rolls down?
Answer: The kinetic energy is greater at the bottom of the hill due to conversion from potential energy.
500: Describe an example of a situation where machines have changed the way we perform tasks in a specific field.
Answer: In healthcare, machines like MRI scanners have revolutionized diagnostics, making it faster and more accurate.
500: What is the efficiency of a machine that has an output work of 300 J and input work of 500 J?
Answer: Efficiency = (output work / input work) x 100 = (300 J / 500 J) x 100 = 60%.