eQuizShow

Work and Machines

Work and power

Question: What is work?
Answer: The transfer of energy to an object by using a force that causes an object to move in the direction of the force.


Question: What is the si unit used to express force and what is the formula for work?
Answer: joules, w=fxd

Question: How is power calculated? What is the si unit for power?
Answer: P=w/t and watts

Question: You and your friend together apply a force 1,000 N to a car, which makes the car roll 10 m in 1 min and 40 s.

A. How much work did you and your friend do together?

B. What was the power output?
Answer: A. W= 1,000 x 10 m= 10,000 J

B. P= 10,000 J / 100 s = 100 W

Question: You lift a chair that weighs 50 N to a height of 0.5 m and carry it 10 m across the room. How much work do you do on the chair?
Answer: 50 N x 0.5 m = 25 J no because once the chair has been lifted the direction and force are in opposite directions.

Mechanical advantage and efficency

Question: What is machine ?
Answer: A device that helps do work by overcoming a force or changing the direction of the applied force.

Question: What is the difference between work output and input?
Answer: Work output the work done by machine and. Input the work done on a machine.

Question: What is the formula for mechanical advantage?
Answer: MA = output force / input force

Question: If you exert a force of 60 N on a machine and the machine exerts 300 N on another object. What is the machine's mechanical advantage?
Answer: MA = 300 N / 60 N = 5

Question: What is the mechanical efficiency of a machine whose work input is 100 J and work output is 30 J?
Answer: ME= 30 J / 100 J x 100 = 30%

Levers

Question: What is a lever?
Answer: A simple machine that pivots at a fixed point.

Question: How do the three types of levers differ from one another?
Answer: Each class of lever involves a different set of mechanical advantage possibilities.

Question: What is the mechanical advantage of a third class lever?
Answer: Less than 1 because the force is decreased. But third class levers increase the distance through which the output force is exerted.

Question: What is the mechanical advantage of a second class lever?
Answer: The mechanical advantage is is greater than 1. The closer. The load is to the fulcrum, the more the force is increased and the greater the mechanical advantage is.

Question: The radius of the weel and axle is 8 times the radius of the axle. What is the mechanical advantage of the wheel and axle?
Answer: MA= 8/1=8

Pulleys

Question: What are the three types of pulleys?
Answer: Fixed,movable, block and tackle

Question: What is a pulley
Answer: A simple machine that consists of a wheel and over which a rope chai of wore passes.

Question: How does a movable pulley?
Answer: Moves up with the load as the load is lifted.

Question: Is an elevator a fixed pulley? How does a fixed pulley work?
Answer: Yes the pulley changed the direction of the force to lift loads.

Question: What does the mechanical advantage depend on for a block and tackle?
Answer: Depends on the number of rope segments?

Compound Machines

Question: Which compoun machine would have the lowest mechanical efficiency: a can opener or a car? Explain your answer
Answer:
CAN OPENER HAS THREE SIMPLE MACHINES WHEEL ANDAXLE AND A WEDGE. A CAR HAS SEVERAL COMPOUND MACHINES. REMEMBER THE MORE COMPOUND MACHINES THE LOWER MECHANICAL EFFICENCY.





Question: What simple machines exsit in a car?
Answer: Wheel and axles,screws,inclined planes, gears,Pulleys

Question: What is a compound machines?
Answer: Consist of 2 or more simple machines.

Question: Why is the work output force of a machine always less than the work input?
Answer: Friction involved in the operation of the machines moving parts causes some of the input energy to be lost as heat.

Question: How is friction useful to breaks on a bike? Explain your answer.
Answer: Prevents people from hurting themselves, breaks has to be on the front and the back of the bike. Other wise someone would fly off. Friction reduces the acceleration of the bike. Answers may vary.