| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 2.94 |
| Score | 0% | 59% |
The standard unit of energy is the:
Volt |
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Joule |
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Watt |
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Horsepower |
The Joule (J) is the standard unit of energy and has the unit \({kg \times m^2} \over s^2\).
Sam can do 50 ft. lb. of work in 2 minutes and 5 seconds. What would Sam have to do to increase his power output?
do the work in 2 minutes |
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do 25 ft. lb. of work in 2 minutes 5 seconds |
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do 100 ft. lb. of work in 4 minutes 12 seconds |
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do the work in 3 minutes |
Power is the rate of doing work or \(\frac{W}{t}\). To increase power, increase the work being done in the same amount of time or do the same amount of work in less time.
Which of the following represents the force a surface exerts when an object presses against it?
friction |
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mass |
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counter force |
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normal force |
Normal force (FN) represents the force a surface exerts when an object presses against it.
If the handles of a wheelbarrow are 3 ft. from the wheel axle, what force must you exert to lift the handles if it's carrying a 270 lb. load concentrated at a point 0.5 ft. from the axle?
90 lbs |
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810 lbs |
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0.83 lbs |
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45 lbs |
This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: Fede = Frdr. Plugging in the variables from this problem yields:
Fe x 3 ft. = 270 lbs x 0.5 ft
Fe = 135 ft-lb. / 3 ft
Fe = 45 lbs
Which of the following will increase the mechanical advantage of a second-class lever?
move the object being lifted closer to the fulcrum |
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move the object being lifted farther away from the fulcrum |
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decrease the length of the lever |
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move the fulcrum between the force and the object being lifted |
A second-class lever is used to increase force on an object in the same direction as the force is applied. This lever requires a smaller force to lift a larger load but the force must be applied over a greater distance. The fulcrum is placed at one end of the lever and mechanical advantage increases as the object being lifted is moved closer to the fulcrum or the length of the lever is increased. An example of a second-class lever is a wheelbarrow.