9. Work & Energy

Which of the following is a likely result of using a more powerful motor to run an elevator?

If you do $90$ joules of work in $30$ seconds, how much power have you generated?

A circuit contains a $5\Omega$ resistor with a current of $2A$ flowing through it. How much power is the resistor dissipating?

If a light draws $220W$ on a $120V$ circuit, what is the current flowing through the light?

A $1500-W$ electric heater is connected to a $120-V$ power line. How much heat energy, in joules, does it produce in $2.0$ hours of operation?

Which of the following correctly defines one watt in terms of base $\mathrm{SI}$ units?

A $10$ horsepower DC motor draws $31$ amps at $300$ volts. What is the efficiency of the motor? ($1$ horsepower = $746$ watts)

If the heating element of an electric dryer is rated at $4.1\mathrm{kW}$ when connected to a $240V$ line, what is the current drawn by the dryer?

What is the power produced by a light bulb with a voltage of $120V$ and a current of $0.045A$?

If a circuit dissipates a reference power $P_0$ under certain conditions, what is the power dissipated by the circuit in terms of $P_0$ if the voltage across the circuit is doubled while the resistance remains constant?

Which of the following best describes what one $W$ is equal to?

Which of the following is the correct SI unit for power?

A driver notices that her 950-kg car, when in neutral, slows down from 95 km/h to 65 km/h in about 7.0 s on a flat horizontal road. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 80 km/h?

The true power is dissipated by the $R$ of any circuit. What does $R$ represent in this context?