Calculate kinetic and potential energy

Answer Key - Grade 11 Science Worksheet

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

1. 1.

   Ari launches a 0.2 kg ball straight up at 7 m/s. Ignoring air, how high above the launch point does it rise? Use g = 9.8 m/s².

   2.5 m
2. 2.

   Esme launches a 3 kg ball straight up at 4.2 m/s. Ignoring air, how high above the launch point does it rise? Use g = 9.8 m/s².

   0.9 m
3. 3.

   A 2 kg cart rolls 4.0 m down a ramp that drops 1.5 m and reaches the bottom at 3.0 m/s. Using g = 9.8 m/s², what is the average friction force, Jun?

   • 5.1 N: (29.4 J − 9 J) ÷ 4.0 m
   • 7.35 N: 29.4 J ÷ 4.0 m, from the drop alone
   • 2.25 N: 9 J ÷ 4.0 m, from the motion alone
   • 13.6 N: (29.4 J − 9 J) ÷ 1.5 m, over the drop
4. 4.

   A ball starts at rest 2.0 m up and ends 0.5 m up, with no friction. Path A is a straight ramp; path B dips to the floor first. Compare the paths, Kira.

   • Same end speed, 6.3 m/s, as both start 2.0 m up
   • Path A ends faster, because its shorter route wastes less energy
   • Same end speed, 5.4 m/s; path B reaches 6.3 m/s at its dip
   • Path B ends faster, because it dips lower and gains more speed
5. 5.

   A motor lifts a 5 kg box 3.0 m in 4.0 s while taking 200 J of electrical energy. Using g = 9.8 m/s², what are the useful power and efficiency, Luz?

   • 147 W useful, 73.5% efficient
   • 50 W useful, 73.5% efficient
   • 36.75 W useful, 73.5% efficient
   • 36.75 W useful, 26.5% efficient
6. 6.

   A 5 kg box rises from a shelf 1.5 m up to a hook 2.1 m up. Milo measures height from the floor; a friend uses a table top 0.9 m up. Results?

   • Neither can find a gain, because their totals disagree
   • Their gains differ by 44.1 J, the table's share of height
   • The floor reading gives a gain of 102.9 J and the table reading 29.4 J
   • Both find a gain of 29.4 J, though their totals differ
7. 7.

   A 0.5 kg ball floats 3 m above the ground over a pit 2 m deep. Using g = 9.8 m/s², what is its gravitational energy measured from the pit floor, Noah?

   • 14.7 J: measured from the ground
   • 24.5 J: 0.5 × 9.8 × 5
   • 9.8 J: 0.5 × 9.8 × 2, the depth of the pit
   • 4.9 J: 0.5 × 9.8 × 1, from 3 − 2
8. 8.

   Pia drops a ball and wants its speed at landing. Why can any zero level be used for the height?

   • The ball's kinetic energy is measured from the zero level too, so the two cancel
   • Every zero level gives the ball the same gravitational energy at the start
   • Only the drop in height counts, and a drop is the same from any zero
   • The zero level must be the floor, so any other choice gives the same answer
9. 9.

   A 0.50 kg pendulum bob is released 0.20 m above its lowest point and rises to 0.18 m on the far side. With g = 9.8 m/s², how much energy did the air remove, Tala?

   • 0.88 J, which is 90% of the starting energy
   • 0.02 J, which is 10% of the starting energy
   • 0.098 J, which is 90% of the starting energy
   • 0.098 J, which is 10% of the starting energy
10. 10.

    A 0.80 kg block slides 1.5 m down a smooth ramp that drops 0.90 m, then squeezes a 980 N/m spring on a smooth floor. How far is the spring squeezed, Zee?

    • 0.085 m: 980 × x² = 0.80 × 9.8 × 0.90
    • 0.155 m: ½ × 980 × x² = 0.80 × 9.8 × 1.5
    • 0.007 m: 980 × x = 0.80 × 9.8 × 0.90
    • 0.12 m: ½ × 980 × x² = 0.80 × 9.8 × 0.90