Power
Grade 11 Science Worksheet - Challenge Me
Circle the best answer, or write your answer on the line.
A turbine must deliver 98000 W of electrical power from water falling 25 m. It is 80% efficient. How many kilograms of water must fall each second, Ari?
A turbine must deliver 4900 W of electrical power from water falling 10 m. It is 40% efficient. How many kilograms of water must fall each second, Bo?
In the power-time graph, how much energy does the motor deliver in all 10 s, Jun?
- 686 J
- 392 J
- 735 J
- 980 J
In the power-time graph, what is the motor's average power over the 10 s, Kira?
Use the picture in question 3.
- 68.6 W
- 73.5 W, the mean of 98 W and 49 W
- 49 W, the final power
- 98 W, the starting power
In the power-time graph, the energy from the first 4 s lifts a 2 kg crate. How high does it rise, Luz?
Use the picture in question 3.
- 196 m
- 35 m
- 10 m
- 20 m
A pulley lets a 20 N pull raise a 100 N load, but the rope moves 5 times as far. Milo says a motor 5 times smaller can do it in the same time. Agree?
- Disagree: the rope is 5 times longer, so the motor needs 5 times more power to pull it
- Agree: a pull 5 times smaller needs a motor that is 5 times less powerful, whatever the rope does
- Disagree: the pull is 5 times smaller but the rope moves 5 times faster, so the power is the same
- Agree: the pulleys supply the extra energy that the heavy load needs, so the motor can be smaller
Air draw a line is the only resistance on a car and grows as the square of its speed. Noah says driving half as fast halves the energy used per kilometer. Agree or disagree?
- Agree: half the speed means half the power, so the energy used for each kilometer is half as much too
- Disagree: power falls to an eighth, so the energy used for each kilometer falls to an eighth as well
- Disagree: drag falls to a quarter, and energy per kilometer is drag times distance, so it falls to a quarter
- Agree: the trip takes twice as long, so the lower power is cancelled and the energy is halved
Read this first
Cart test (example data)
Speed (m/s) Power (W) 2 12 4 96 6 324 A cart is pulled at three steady speeds. Pia says the resistance force is the same at every speed. Does the table support the claim?
- No: power ÷ speed gives 6 N, 24 N and 54 N, so the force grows with speed
- No: power rises 27 times, so the force rises 27 times
- Yes: at a steady speed the pull is constant, so the force is constant
- Yes: power ÷ speed gives 6 N at each speed
A lift must raise an 80 kg load 12 m in 20 s at steady speed. Its motor turns 70% of the power it draws into lifting. Which is the smallest rating that works, Ren?
- 750 W
- 600 W
- 500 W
- 1,000 W
A 60 W motor turns 80% of its power into pulling. It pulls a 5 kg cart up a smooth 30° ramp at steady speed. How fast does the cart rise along the ramp, Tala?
- 2.45 m/s
- 3.06 m/s
- 1.96 m/s
- 0.98 m/s