Homework Answers

Here are the answers to some homework questions set in January 2020.

3. same

4. 10 x 10 = 100 J

5. 100 / 0.5 = 200 W, 100 / 1 = 100 W

7. 100 J

26. A (left) has momentum = 800 kg x 1.0 = 800 kg m/s, kinetic energy = 0.5 x 800 kg x (1 m/s)² = 400 J

B (center) has momentum = 1000 kg x 2.0 = 2000 kg m/s, kinetic energy = 0.5 x 1000 kg x (2 m/s)² = 2000 J

C (right) has momentum = 90 kg x 8.0 = 720 kg m/s, kinetic energy = 0.5 x 90 kg x (8 m/s)² = 2880 J

So, listed in order of decreasing momentum: BAC

listed in order of decreasing k.e. : CBA

34. 20 x 3.5 = 70 J

37. 70 J / 0.5 s = 140 W

6. kinetic and potential

38. GPE = mgh = 1 x 10 x 4 = 40 J

GPE = mgh = 1 x 10 x 8 = 80 J

39. GPE = mgh = 20 x 10 x 2 = 400 J