MASS Mechanical Concepts — Questions and Answers
Question 1: The force required to move 550 pounds one foot in one second is usually referred to as:
- Horsepower (Correct answer)
- Volts
- Joule
- Meters
Correct answer: Horsepower
Horsepower is a unit of power, historically defined by James Watt. One mechanical horsepower is precisely the power needed to lift 550 pounds a distance of 1 foot in 1 second. This definition directly matches the scenario described in the question.
Question 2: Mark must pull a truck for 1 minute. The truck weighs 115.5 tons. What is the bare minimum in terms of horsepower?
- 7hp (Correct answer)
- 10hp
- 14hp
- 23hp
Correct answer: 7hp
Horsepower is a measure of power, defined as the rate at which work is done. One horsepower is equivalent to lifting 33,000 pounds one foot in one minute. If the truck weighs 115.5 tons (which is 231,000 pounds), and assuming the 'pull' implies lifting it 1 foot in 1 minute, the required horsepower would be 231,000 ft-lbs / 33,000 ft-lbs/min/hp = 7 horsepower.
Question 3: 5,968 watts are needed by an elevator motor to drive the elevator. How many horsepower does the elevator's electric motor have?
- 8 (Correct answer)
- 16
- 9
- 20
Correct answer: 8
To convert watts to horsepower, you divide the number of watts by the conversion factor of 746 watts per horsepower. Therefore, an elevator motor requiring 5,968 watts has 5968 / 746 = 8 horsepower.
Question 4: A pipe connects two identical covered liquid containers. How much force will the connecting pipe apply if one side receives 12 lbs of force?
- 12 lbs (Correct answer)
- 16 lbs
- 18 lbs
- 20 lbs
Correct answer: 12 lbs
According to Pascal's Principle, pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel. Since the two liquid containers are identical, they have the same cross-sectional area. Therefore, if 12 lbs of force is applied to one side, an equal force of 12 lbs will be transmitted through the liquid to the other side and applied by the connecting pipe.
Question 5: An engine produces 90hp and is 90% efficient. So, how much horsepower is being lost due to inefficiency?
- 10hp (Correct answer)
- 20hp
- .20hp
- .10hp
Correct answer: 10hp
An engine's efficiency indicates the percentage of input power that is converted into useful output power. If an engine produces 90 horsepower at 90% efficiency, it means 90 hp represents 90% of the total power input. To find the total input power, divide the output power by the efficiency (90 hp / 0.90 = 100 hp). The power lost due to inefficiency is the difference between the input and output power, which is 100 hp - 90 hp = 10 hp.
Question 6: Daryl is using a pulley system to lift a 100-pound box, but the pulleys are only 50% efficient. How many pounds of force is he using to move the box?
- 200lbs (Correct answer)
- 100lbs
- 300lbs
- 400lbs
Correct answer: 200lbs
Efficiency in a pulley system means that only a percentage of the input force is effectively used to lift the load, with the rest lost to friction. If the pulley system is 50% efficient and Daryl needs to lift a 100-pound box (representing the useful output force), he must apply twice that amount of force as input. Therefore, Daryl is using 100 pounds / 0.50 efficiency = 200 pounds of force.
Question 7: How much work did a rock climber put in if he used 660 newtons to climb a 30 meter cliff?
- 19,800J (Correct answer)
- 15,600J
- 20,000J
- 10,400J
Correct answer: 19,800J
Work done is calculated by multiplying the force applied by the distance over which the force is applied (W = F * d). In this case, the rock climber applied a force of 660 Newtons over a distance of 30 meters. Therefore, the work done is 660 N * 30 m = 19,800 Joules.
MASS Mechanical Concepts
The force required to move 550 pounds one foot in one second is usually referred to as: