Mechanical Comprehension Practice Test 11

Correct answer: D — All of the above

Generators convert mechanical rotational energy into electrical energy and can be driven by various prime movers, including steam turbines, internal combustion diesel engines, and wind turbines.

Correct answer: A — 4,800 joules

Work performed is calculated as Force × Distance: $$W = 1{,}200\text{ N} \times 4\text{ m} = 4{,}800$$ Joules.

Correct answer: A — 6

Mechanical Advantage (MA) = Load / Effort = 600 lb / 100 lb = 6. This means 6 supporting rope segments (or pulleys in an ideal system) share the load.

Correct answer: A — 5 feet

Using the conservation of work (Input Work = Output Work): Force × Ramp Length = Weight × Height. So, 100 lb × 20 ft = 400 lb × Height => $$2{,}000 = 400 \times \text{Height} \Rightarrow \text{Height} = 5$$ feet.

Correct answer: A — 10 rpm

For chain-linked sprockets, the linear speed of the chain is identical for all sprockets. The rotational speed ratio depends directly on the ratio of driver diameter to driven diameter: $$\text{Speed}_C = \text{Speed}_A \times (\text{Diameter}_A / \text{Diameter}_C) = 40\text{ rpm} \times (3\text{ in} / 12\text{ in}) = 10$$ rpm.

Correct answer: A — 4 meters

Mechanical Advantage (MA) of a lever is calculated as Effort Arm / Load Arm. Therefore, Load Arm = Effort Arm / MA = $$12\text{ meters} / 3 = 4$$ meters.

Correct answer: A — 24 rotations

Gear teeth ratio is inversely proportional to rotation count: $$N_A \times \text{Turns}_A = N_B \times \text{Turns}_B$$. $$30 \times 12 = 15 \times \text{Turns}_B \Rightarrow \text{Turns}_B = \frac{360}{15} = 24$$ rotations.

Correct answer: A — Hydrostatic pressure

Hydrostatic pressure refers specifically to the static pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity.

Correct answer: A — It allows air to enter and equalize internal pressure with outside atmospheric pressure.

An open vent allows atmospheric air to fill the space left by liquid leaving the container, preventing a partial vacuum from forming inside that would oppose liquid flow.

Correct answer: A — 300 N

Mechanical Advantage of Lever 1 = $$\frac{10}{2} = 5$$.

Mechanical Advantage of Lever 2 $$= \frac{12}{3} = 4$$.

Total compound MA $$= 5 \times 4 = 20$$. Output Force = Input Force × Total MA $$= 15\text{ N} \times 20 = 300\text{ N}$$

Correct answer: A — $$3.96\text{ m/s}$$

At the top, Potential Energy = mgh = $$2 \times 9.8 \times 0.8 = 15.68\text{ J}$$.

At the lowest point, all PE converts to Kinetic Energy $$= (\frac{1}{2})mv^2$$.

So, $$15.68 = (\frac{1}{2})(2)v^2 \Rightarrow v^2 = 15.68 \Rightarrow v \approx 3.96\text{ m/s}$$.

Correct answer: A — 60 rpm, Clockwise

The idler Gear B changes direction twice (A clockwise -> B counter-clockwise -> C clockwise), so C turns clockwise. Speed ratio: $$\text{Speed}_C = \text{Speed}_A \times (\text{Teeth}_A / \text{Teeth}_C) = 120\text{ rpm} \times (\frac{16}{32}) = 60$$ rpm.

Correct answer: A — 100,000 N

Pressure is defined as Force / Area $$(P = \frac{F}{A})$$. Rearranging gives Force = Pressure × Area $$= 50{,}000\text{ N/m}^2 \times 2\text{ m}^2 = 100{,}000\text{ N}$$

Correct answer: A — Velocity increases through the restriction, and downstream pressure drops.

According to the continuity equation and Bernoulli's principle, narrowing the flow passage increases local fluid velocity while causing a pressure drop (throttling effect) downstream.