Power

Answer Key - Grade 11 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   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?

   500 kg/s
2. 2.

   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?

   125 kg/s
3. 3.

   A turbine must deliver 44100 W of electrical power from water falling 30 m. It is 75% efficient. How many kilograms of water must fall each second, Esme?

   200 kg/s
5. 4.

   In the power-time graph, how much energy does the motor deliver in all 10 s, Jun?

   • 980 J
   • 686 J
   • 735 J
   • 392 J
6. 5.

   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 4.

   • 10 m
   • 35 m
   • 20 m
   • 196 m
7. 6.

   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: the trip takes twice as long, so the lower power is cancelled and the energy is halved
   • Disagree: power falls to an eighth, so the energy used for each kilometer falls to an eighth as well
   • Agree: half the speed means half the power, so the energy used for each kilometer is half as much too
   • Disagree: drag falls to a quarter, and energy per kilometer is drag times distance, so it falls to a quarter

8. Read this first

   Cart test (example data)

   Speed (m/s)	Power (W)
   2	12
   4	96
   6	324

9. 7.

   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 rises 27 times, so the force rises 27 times
   • No: power ÷ speed gives 6 N, 24 N and 54 N, so the force grows with speed
   • Yes: at a steady speed the pull is constant, so the force is constant
   • Yes: power ÷ speed gives 6 N at each speed
10. 8.

    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
    • 500 W
    • 600 W
    • 1,000 W
11. 9.

    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
    • 1.96 m/s
    • 3.06 m/s
    • 0.98 m/s
12. 10.

    A winch lifts a load. A new job has a load twice as heavy, raised three times as high, in the same time. How does the power needed change, Zee?

    • 3 times as much
    • 6 times as much
    • 2 times as much
    • 5 times as much