| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.23 |
| Score | 0% | 65% |
Which of the following surfaces would have the highest coefficient of friction?
marble |
|
ice |
|
steel |
|
concrete |
Coefficient of friction (μ) represents how much two materials resist sliding across each other. Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.
Which of the following will increase the mechanical advantage of a second-class lever?
move the object being lifted closer to the fulcrum |
|
move the fulcrum between the force and the object being lifted |
|
decrease the length of the lever |
|
move the object being lifted farther away from the fulcrum |
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.
| 602 lbs. | |
| 600 lbs. | |
| 660 lbs. | |
| 606 lbs. |
The mechanical advantage (MA) of a block and tackle pulley is equal to the number of times the effort force changes direction. An easy way to count how many times the effort force changes direction is to count the number of ropes that support the resistance which, in this problem, is 6. With a MA of 6, a 100 lbs. effort force could lift 100 lbs. x 6 = 600 lbs. resistance.
| 0.6 | |
| 2.1 | |
| 0.2 | |
| 2.6 |
Mechanical advantage (MA) is the ratio by which effort force relates to resistance force. If both forces are known, calculating MA is simply a matter of dividing resistance force by effort force:
MA = \( \frac{F_r}{F_e} \) = \( \frac{2 ft.}{3.33 ft.} \) = 0.6
In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.6 units of resistance force. However, a third class lever like this isn't designed to multiply force like a first class lever. A third class lever is designed to multiply distance and speed at the resistance by sacrificing force at the resistance. Different lever styles have different purposes and multiply forces in different ways.
Which of the following is the formula for torque?
τ = F/r2 |
|
τ = r/F |
|
τ = rF |
|
τ = F/r |
Torque measures force applied during rotation: τ = rF. Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).