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?

   • 735 J
   • 392 J
   • 686 J
   • 980 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.

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

   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?

   • Agree: the pulleys supply the extra energy that the heavy load needs, so the motor can be smaller
   • Agree: a pull 5 times smaller needs a motor that is 5 times less powerful, whatever the rope does
   • Disagree: the rope is 5 times longer, so the motor needs 5 times more power to pull it
   • Disagree: the pull is 5 times smaller but the rope moves 5 times faster, so the power is the same
8. 7.

   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
   • 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
9. 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
   • 600 W
   • 500 W
   • 1,000 W
10. 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?

    • 1.96 m/s
    • 2.45 m/s
    • 0.98 m/s
    • 3.06 m/s
11. 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?

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