Page 59 - SP015 Past Years PSPM Chapter 1 -5 Ver.2020

PSPM SP015

FINAL ANSWER FOR CHAPTER 5: WORK, ENERGY AND POWER

1. Work done is the product of the component of the force parallel to displacement and the displacement of
the body.
Work done is the scalar product of force and displacement.
2 -2
SI unit of work is J or N m or kg m s .

2. (b) T = 227 N (c) W = 0 J
-2
3. Since speed is constant, a = 0 m s so F net = 0 N thus work, W = 0 J
4. W = 93 J

5. (a) Kinetic energy is the energy of a body due to its motion.
(b) Elastic potential energy is the energy due to compression or extension of elastic material.

6. Factors that contribute to the potential energy of an object are position and state @ condition.

7. Similarity: Both are energy or both have same unit.
Difference: Kinetic energy is energy possess by an object due to its motion. Potential energy is the
energy possess by an object due to its position or state.

8. Principle of conservation of energy states that the total energy is conserved for a closed system.

9. Work-energy theorem states that work done is equal to the change in energy.
10. h = 0.35 m

11. E loss = 2240 J
-1
12. v = 2.33 m s
4
5
13. (a) (ii) s = 76.36 m (b) (i) W = –7.49  10 J (ii) F = –6.24  10 N
-1
14. v = 2.83 m s
15. (a) W = 128 J (b) U Y = 1471.5 J
16. W net = 3320 J
17. W = 52.5 J
-1
18. (a) u = 5.42 m s (b) h max = 1.5 m

19. (a) U = 0.05 J
(b) Frictionless track  no work done against friction or no heat dissipation
Horizontal plane  no change in potential energy
Energy conserved or W = K  K = constant  v = constant
-1
(c) v = 6.79 m s

-1
20. v = 3.94 m s

21. (a) W = 0.80 J (b) U s = 0.80 J
-1
22. (a) U = 1569.6 J (b) v B = 19.81 m s
-1
23. (a) W g = 2.34 J (b) v = 3.84 m s
-1
24. (a) K = 0.04 J (b) k = 800 N m
25. F = 2.08 N
26. K f = 117.72 J

-1
27. (a) v = 13.62 m s
(b) If the mass of the block is increased, the final speed of the block will be the same. Speed of the block
does not depend on mass of the block in work-energy equation.

-1
28. u = 4.43 m s
29. K = 66 J
-1
30. v = 2.7 m s

-2
-1
31. (a) a = 3.38 m s (b) T = 12.9 N (c) K = 9.12 J (d) v = 2.01 m s
-1
33. (a) F = 1 N (b) k = 2000 N m
4
4
34. (a) P = 1.77  10 W (b) P = 6.37  10 W
59