A constant horizontal force of 36 N pulls a crate 5.0 m along a smooth floor in the direction of the force. How much work is done by this force?
Energy
Question · Easy
A 3.0 kg ball moves at 4.0 m/s. What is its kinetic energy?
A 6.0 kg bag of taro is lifted 2.5 m onto a truck. Take g = 10 m/s². What is the gain in gravitational potential energy?
A motor does 900 J of useful work in 15 s. What is its useful power output?
A machine takes in 250 J of energy and delivers 100 J of useful work. What is its efficiency?
A battery-powered fan is switched on and the blades start to turn. Which energy transfer is the main useful transfer?
What is the SI unit of work and of energy?
A student pushes a trolley with a force of 25 N for 8.0 m in the same direction as the force. How much work does the student do on the trolley?
A 2.0 kg coconut speeds up from 3.0 m/s to 7.0 m/s. What is the increase in its kinetic energy?
Question · Medium
A 50 kg student stands on a balcony 8.0 m above the ground. Take g = 10 m/s². What is her gravitational potential energy relative to the ground?
A winch lifts an 80 kg outboard motor vertically at a constant speed of 0.40 m/s. Take g = 10 m/s². What is the useful power output of the winch?
An electric motor is rated at 400 W and delivers 280 W of useful mechanical power. What is its efficiency?
A box is dragged 12 m across a rough floor against a constant friction force of 15 N. How much work is done against friction?
A 1.5 kW heater is switched on for 4.0 minutes. How much energy does it transfer?
A spring of spring constant 250 N/m is compressed by 8.0 cm. How much elastic potential energy is stored in the spring?
A 0.50 kg mango falls from rest from a height of 5.0 m. Take g = 10 m/s² and neglect air resistance. What is its speed just before it hits the ground?
How much thermal energy is needed to raise the temperature of 0.40 kg of water by 15 °C? The specific heat capacity of water is 4200 J/(kg·°C).
A lamp is 25% efficient. If it takes in 80 J of electrical energy, how much energy is wasted (not useful light)?
A 4.0 kg parcel is lowered 3.5 m at constant speed. Take g = 10 m/s². How much work is done by the weight of the parcel?
A crane does 2.4 × 10⁴ J of useful work in 20 s. What is its useful power?
A 70 kg athlete runs up a staircase of vertical height 5.0 m in 7.0 s. Take g = 10 m/s². What is her average useful power against gravity?
Question · Hard
A 600 W pump lifts 40 kg of water a vertical height of 12 m in 10 s. Take g = 10 m/s². What is the efficiency of the pump?
A 900 kg car travelling at 16 m/s is brought to rest by a constant braking force of 3600 N. What is the braking distance?
A 0.20 kg stone is thrown from a cliff 15 m high at 10 m/s. Take g = 10 m/s². What is the total mechanical energy of the stone at the instant it is thrown, relative to the foot of the cliff?
A 1.5 kW kettle heats 0.50 kg of water from 20 °C to 100 °C. The specific heat capacity of water is 4200 J/(kg·°C). Assume no energy is lost. How long does the heating take?
A 12 V battery is connected across a 6.0 Ω resistor. What is the current in the resistor?
Electricity
A current of 0.25 A flows through a 48 Ω resistor. What is the potential difference across the resistor?
Three resistors of 2.0 Ω, 8.0 Ω and 10 Ω are connected in series. What is the total resistance?
Two 10 Ω resistors are connected in parallel. What is the combined resistance?
A steady current of 2.5 A flows for 40 s. How much charge passes a point in the circuit?
A lamp is connected to a 230 V supply and takes a current of 2.0 A. What is the power of the lamp?
Which statement correctly defines electric current?
A 6.0 Ω resistor and a 3.0 Ω resistor are connected in parallel. What is the combined resistance?
A 4.0 Ω resistor is in parallel with a 12 Ω resistor. This combination is then connected in series with a 7.0 Ω resistor. What is the total resistance?
An 18 V battery is connected across a 3.0 Ω resistor in series with a 6.0 Ω resistor. What is the current in the circuit?
A 9.0 V battery is connected across a 2.0 Ω resistor in series with a 4.0 Ω resistor. What is the potential difference across the 2.0 Ω resistor?
A 24 V supply is connected across an 8.0 Ω resistor in parallel with a 12 Ω resistor. What is the total current drawn from the supply?
A current of 3.0 A flows through a 4.0 Ω resistor. What is the power dissipated in the resistor?
A 120 V heater takes a current of 4.0 A for 30 s. How much electrical energy is transferred?
A charge of 8.0 mC passes a point in a wire in 4.0 ms. What is the current?
Three 12 Ω resistors are connected in parallel. What is the combined resistance?
A 3.0 kW cooker is used for 2.0 hours. How much energy does it use?
The I–V graph for a metal filament lamp curves so that I increases more slowly than V at higher voltages. What is the best explanation?
A 48 W lamp operates from a 12 V supply. What current does the lamp take?
Which change increases the resistance of a uniform metal wire at constant temperature?
A 12 V battery is connected to two 6.0 Ω resistors in parallel, and that combination is in series with a 3.0 Ω resistor. What is the current in one of the 6.0 Ω resistors?
An 80 Ω heating element is connected to a 240 V mains supply. What is the power of the heater?
A 10 Ω resistor and a 40 Ω resistor are connected in parallel across a 20 V supply. What is the total power dissipated in both resistors?
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