Compare devices that change energy from one form to another

Answer Key - Grade 11 Science Worksheet - Building Confidence

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

1. 1.

   Ari's motor takes 500 W and lifts a 20 kg load 3 m in 10 s. With g = 9.8 m/s², what is its efficiency in percent?

   11.8 %
2. 2.

   Esme's motor takes 200 W and lifts a 12 kg load 5 m in 4 s. With g = 9.8 m/s², what is its efficiency in percent?

   73.5 %
3. 3.

   A fan takes in 800 J. It gives out 40 J of sound and 520 J of thermal energy; the rest is moving air. What are the useful energy and efficiency, Jun?

   • 240 J useful, 3.3% efficient
   • 240 J useful, 30% efficient
   • 280 J useful, 35% efficient
   • 560 J useful, 70% efficient
4. 4.

   A bar chart shows 250 J in, 90 J of light and 130 J of thermal energy out. How much must the sound bar show, Kira?

   • 30 J, since 250 − 90 − 130 = 30
   • 160 J, the input less the light
   • 340 J, the sum of the three bars shown
   • 220 J, the light plus the thermal energy
5. 5.

   Which energy chart in the table cannot be right, Luz?

   • Z: more than half of its energy is wasted
   • No chart is wrong: any may lose some energy for good
   • X: its outputs exactly match its input
   • Y: its outputs add to 350 J, more than the 300 J in
6. 6.

   Which list gives the energy forms in order in a coal power plant, Milo?

   • Thermal, chemical, kinetic, electrical
   • Chemical, thermal, electrical, kinetic
   • Chemical, kinetic, thermal, electrical
   • Chemical, thermal, kinetic, electrical
7. 7.

   Which list gives the energy forms in order in a hydroelectric dam, Noah?

   • Kinetic, gravitational, electrical
   • Gravitational, kinetic, electrical
   • Chemical, kinetic, electrical
   • Gravitational, electrical, kinetic
8. 8.

   An electric car slows by regenerative braking. Which list gives the energy forms in order, Pia?

   • Chemical, electrical, kinetic in the wheels
   • Kinetic, electrical, chemical (battery)
   • Kinetic, thermal, chemical in the battery
   • Kinetic, electrical, thermal in the brake pads
9. 9.

   A lamp takes in 100 J and gives out 12 J of light. What happens to the other 88 J, Tala?

   • It spreads out as thermal energy in the room
   • It is used up in the lamp and disappears
   • It goes back along the wire into the wall socket
   • It turns into light that our eyes cannot see
10. 10.

    An inventor says a motor is 110% efficient. What is wrong with the claim, Zee?

    • Useful output cannot exceed the energy put in
    • Nothing is wrong, if the motor is well oiled
    • The percent alone is wrong: it should read 11%
    • Nothing is wrong, if the motor also stores energy