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Word Knowledge

After Kal's father revoked his allowance, he had no money for the movies.

rescind

To cancel by taking back.

General Science

A subatomic particle found in the nucleus of an atom. It carries no electric charge. This desribes which of the following?

neutron

A neutron is a subatomic particle found in the nucleus of an atom. It is neutral as it carries no electric charge.

Automotive Information

Too much fuel results in a __________ air-fuel mixture that burns quicker and cooler.

rich

The stoichiometric ratio defines the proper ratio of air to fuel necessary so that an engine burns all fuel with no excess air. For gasoline fuel, the stoichiometric ratio is about 14.7:1 or for every one gram of fuel, 14.7 grams of air are required. Too much air results in a lean air-fuel mixture that burns more slowly and hotter while too much fuel results in a rich mixture that burns quicker and cooler.

Word Knowledge

Jennifer's outspoken criticism of the meal disoncerted the waiter.

unnerve

To throw into confusion.

Word Knowledge

Rashid made the untenable statement that George Washington was the second president of the United States.

baseless

Not able to be defended.

Shop Information

Which of the following statements about drill bits is not true?

drill bits are primarily left-handed

Drill bits remove material to create holes. They come in a variety of sizes, maxing out at ¼" for woodworking and ½" for metalworking. The majority of drill bits are right-handed which means they cut while rotating in a clockwise direction.

Automotive Information

Ignition timing is measured in number of degrees:

before top dead center

Ignition timing defines the point in time at the end of the compression stroke that the spark plug fires. Measured in number of degrees before top dead center (BTDC), the exact point that the spark plugs initiate combustion varies depending on the speed of the engine. The timing is advanced (the spark plugs fire a few more degrees BTDC) when the engine is running faster and retarded when it's running slower.

Automotive Information

What type of energy does an automotive battery produce?

direct current

An automotive battery produces direct current for use by automotive systems.

Word Knowledge

Aerate most nearly means:

oxygenate

To supply with air.

Mechanical Comprehension

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?

0.88

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 (E_a) by the length of the resistance arm (R_a):

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 R_ad_a = R_bd_b where a and b are the two points at which effort/resistance is being applied to the lever.

In this problem, R_a and R_b 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 E_a by R_a to get the mechanical advantage.