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.

   Bo's motor takes 300 W and lifts a 50 kg load 2 m in 5 s. With g = 9.8 m/s², what is its efficiency in percent?

   65.3 %
3. 3.

   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 %
4. 4.

   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?

   • 280 J useful, 35% efficient
   • 560 J useful, 70% efficient
   • 240 J useful, 30% efficient
   • 240 J useful, 3.3% efficient
5. 5.

   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
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?

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

   A phone charger feels warm while it charges. Where does that thermal energy come from, Ren?

   • The warmth is sound energy that has changed form
   • The charger destroys part of the electrical energy put in
   • Some input electrical energy becomes thermal energy
   • The battery makes new thermal energy out of nothing
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?

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