How work is necessarily a positive quantity

Question

Assignment:

Mark the following statements true or false. If you mark it false, tell why it is false and how it could be changed to make it true.

Question 1. If a force F acts on a particle of mass m which is moving at a speed v, we define the work done to be the change in the quantity 1/2mv^2.

Question 2. Work is necessarily a positive quantity.

Question 3. The definition of work as force times distance moved is generally valid only for one-dimensional problems.

Question 4. The dimensions of work are the same as those of energy.

Question 5. Joule, foot-pound, watt-second, and erg are all units of energy.

Question 6. If several forces act on a particle, the total work done by all of them is the work done by the net resultant force.

Question 7. The theorem stating that the net work done on a particle is equal to its change of kinetic energy is generally valid only for one-dimensional problems.

Question 8. In the most general case, the work-energy theorem states that the  net work done, over and interval, by the resultant force on a particle is equal to the change in the particle’s kinetic energy.

Question 9. An object, starting from rest, slides down a frictionless hill;  its speed at the bottom depends only on the height, and not the shape of the hill.

Question 10. The work done on an object by frictional forces is always negative.

Question 11. A heavy crate is dragged across a rough floor from point A to point B; the work done on it is independent of the path taken from A to B.

Question 12. A heavy crate is dragged across a rough floor from point A to point B; the work done by the normal force of the floor on the crate is independent of the path taken from A to B.

Question 13. If a 50-lb box is lifted, slowly and steadily, 4ft above the floor, the work done on the box is 200 ft-lb.

Question 14. If  a 50-lb box is lifted, slowly and steadily, 4ft above the floor, the box’s kinetic energy is increased by 200 ft-lb.

Question 15. If a 50-lb box is lifted, slowly and steadily, 4ft above the floor, the box’s potential energy is increased by 200 ft-lb.

Question 16. If a 50-lb box is lifted, slowly and steadily, 4ft above the floor, the work done on the box by gravity is -200ft-lb.

Question 17. A block slides down an incline; conservation principles say that the work done on the block by the incline is equal to the work done on the incline by the block.

Question 18. The following units all measure the same physical quantity:  foot-pound/second, horsepower, watt, joule.

Question 19. Potential energy can be regarded as work that is “stored”by being done against some force.

Question 20. Potential energy and work have the same dimensions.

Question 21. Potential energy can be unambiguously associated only with a conservative force.

Question 22. If  a body is acted upon only by conservative forces, the sum of its potential  and kinetic energy is constant.

Question 23. A conservative force is one such that the work it does on a particle in moving it along any path is zero.

Question 24. Friction is a non-conservative force.

Question 25. If a particle is acted upon only by conservative forces, then whenever it returns to its initial position, it has its initial velocity.

Question 26. In one dimension, any force which depends only on the position of the particle is conservative.

Question 27. The work done by a conservative force on a particle is equal to the increase of  the corresponding potential energy of the particle.

Question 28. The absolute value of potential energy is indeterminate.

Question 29. A force is non conservative if the work done by it in moving a particle between two given points depends on the path taken.

Question 30. The force of earths gravity does positive work on any satellite in a circular orbit around the earth.

Question 31. As a simple pendulum swings back and forth, the tension in the supporting cord does work on the pendulum.

Question 32. The total mechanical energy of an object is conserved if the net force on the body is zero.

Question 33. The work done on a system by non-conservative forces is equal to the change in its total mechanical energy.