Energy conversion devices Transitional Reasoning Download PDF
10 Physics practice questions on Energy conversion devices. Questions that build towards applied reasoning.
Questions
- 1.
An electromagnetic aircraft launch system acts as a high-power energy conversion device, using linear induction motors to accelerate naval aircraft along a runway. During a test launch, the system accelerates a 12 000 kg aircraft from rest to a takeoff speed of 60 m/s in a time interval of 2.0 s. If the launcher converts stored electrical energy from its capacitor banks into the aircraft's mechanical kinetic energy with an overall efficiency of 60%, what total electrical energy must be supplied by the capacitors, and what average electrical power does the system draw during the launch?
- 2.
A compressed-air energy storage facility uses an expander-generator unit as an energy conversion device to generate electricity during peak grid demand. The expanding air supplies pneumatic power to the unit at a constant rate of 40 kW, and the system converts this mechanical energy into electricity with an overall efficiency of 65%. Over a continuous generation cycle of 30 minutes, what total electrical energy is delivered to the grid, and at what average rate is energy dissipated as waste heat?
- 3.
A gravitational energy storage facility is designed to deliver a steady electrical power output of 60 kW for 10 minutes to stabilize a local power grid during peak demand. The system operates by slowly lowering a dense suspended block through a vertical descent of 250 m at a constant speed, driving a generator with an overall conversion efficiency of 80%. Taking the acceleration due to gravity as , what mass must the suspended block have, and what total thermal energy is dissipated by the system during this discharge period?
- 4.
A commuter tram with a total mass of 24 000 kg slows down smoothly on a horizontal track from an initial speed of 20 m/s to 10 m/s over a duration of 15 s. During this braking maneuver, its regenerative braking system acts as an energy conversion device, converting 70% of the lost mechanical kinetic energy into useful electrical energy delivered back to the power grid. What total electrical energy is supplied to the grid, and what is the average electrical power delivered during this braking phase?
- 5.
An automated sorting facility uses an electric belt conveyor to move parcels horizontally at a steady speed of 2.5 m/s. To counteract mechanical friction, the drive mechanism applies a constant horizontal tractive force of 720 N to the belt. The electric motor system drives the conveyor with an overall energy efficiency of 75%. Over a continuous operating period of 50 minutes, what total electrical energy does the motor consume from the mains, and how much energy is dissipated as waste heat?
- 6.
An autonomous deep-sea probe is powered by a radioisotope thermoelectric generator that steadily converts heat from a decaying radioactive source into electricity. The radioisotope source releases thermal energy at a constant rate of 600 W, and the thermoelectric module converts this heat into electrical power with an efficiency of 8.0%. If the probe's essential sensors continuously draw 36 W of electrical power, what surplus electrical power is available to recharge its secondary storage cells, and at what rate is unconverted heat rejected into the ocean?
- 7.
A stationary flywheel energy storage unit captures and stores 500 kJ of rotational kinetic energy from an industrial braking system. When discharging to supply emergency backup power, the unit delivers 350 kJ of useful electrical energy to connected loads over a duration of 25 seconds. What is the overall energy efficiency of this storage device, and at what average rate is energy dissipated as waste during the discharge cycle?
- 8.
An electric utility vehicle's powertrain converts stored electrical energy from a battery pack into mechanical work to ascend a slope. To maintain a constant speed, the drive wheels must deliver a useful mechanical power of 36 kW. The electric motor operates with an energy efficiency of 90%, and the mechanical transmission connecting the motor to the wheels operates with an efficiency of 80%. What electrical power must the battery pack supply, and at what rate is energy dissipated as heat across the entire powertrain?
- 9.
A rural irrigation facility uses a solar-powered pumping system where a photovoltaic array receives incident sunlight at a total radiant power of 1500 W. The array converts this solar energy into electrical power with an efficiency of 20% and supplies it directly to an electric motor driving a water pump. If the motor-pump unit delivers useful mechanical power to the flowing water at a rate of 210 W, what are the overall efficiency of the entire solar pumping system and the efficiency of the motor-pump unit alone?
- 10.
An engineer tests an electric winch designed to lift cargo at a construction site. Operating at a constant potential difference of 200 V, the motor draws a current of 4.0 A to vertically raise a 48 kg container by 10 m at a constant speed in 8.0 s. Assuming the acceleration due to gravity is 10 m/s2, what is the overall energy efficiency of this lifting system and the rate at which energy is dissipated as waste heat and sound?