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Sample Practice Test Questions
If the green box is 8 ft. from the fulcrum and a certain force applied 7 ft. from the fulcrum at the blue arrow balances the lever, what is the mechanical advantage?
Because this lever is in equilibrium, we know that the effort force at the blue arrow is equal to the resistance weight of the green box. For a lever that's in equilibrium, one method of calculating mechanical advantage (MA) is to divide the length of the effort arm (Ea) by the length of the resistance arm (Ra):
MA = \( \frac{E_a}{R_a} \) = \( \frac{7 ft.}{8 ft.} \) = 0.88
When a lever is in equilibrium, the torque from the effort and the resistance are equal. The equation for equilibrium is Rada = Rbdb where a and b are the two points at which effort/resistance is being applied to the lever.
In this problem, Ra and Rb are such that the lever is in equilibrium meaning that some multiple of the weight of the green box is being applied at the blue arrow. For a lever, this multiple is a function of the ratio of the distances of the box and the arrow from the fulcrum. That's why, for a lever in equilibrium, only the distances from the fulcrum are necessary to calculate mechanical advantage.
If the lever were not in equilibrium, you would first have to calculate the forces and distances necessary to put it in equilibrium and then divide Ea by Ra to get the mechanical advantage.
Materials like metals that transfer heat efficiently are called:
conductors
Heat is always transferred from warmer to cooler environments and conduction is the simplest way this transfer can occur. It is accomplished through direct contact between materials and materials like metals that transfer heat efficiently are called conductors while those that conduct heat poorly, such as plastic, are called insulators.
The steering __________ transfers the motion of the steering gear output shaft to the steering arms that turn the wheels.
linkage
The steering linkage is a system of pivots and connecting parts between the steering gear and the control arms. The steering linkage transfers the motion of the steering gear output shaft to the steering arms that turn the wheels.
If A = 10 ft., B = 1 ft., C = 9 ft., the green box weighs 50 lbs. and the blue box weighs 60 lbs., what does the orange box have to weigh for this lever to balance?
fAdA = fBdB + fCdC
For this problem, this equation becomes:
50 lbs. x 10 ft. = 60 lbs. x 1 ft. + fC x 9 ft.
500 ft. lbs. = 60 ft. lbs. + fC x 9 ft.
fC = \( \frac{500 ft. lbs. - 60 ft. lbs.}{9 ft.} \) = \( \frac{440 ft. lbs.}{9 ft.} \) = 48.89 lbs.
The steering wheel of a car is an example of which type of simple machine?
wheel and axle
A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.
This circuit diagram represents a(n):
series circuit
A series circuit has only one path for current to flow. In a series circuit, current (I) is the same throughout the circuit and is equal to the total voltage (V) applied to the circuit divided by the total resistance (R) of the loads in the circuit. The sum of the voltage drops across each resistor in the circuit will equal the total voltage applied to the circuit.