Simple Machines and Power

If Tracy puts 482 J of work into the system, but only 437 J are used to elevate the block, what is the efficiency of the inclined plane?

91%

The wheel and axle below has an ideal mechanical advantage of 5.Accounting for friction, 45 N applied to the outside of the wheel over one rotation generates 213 N of force at the axle. What is the actual mechanical advantage of the wheel and axle?

4.7

Which of the following simple machines does a can opener have? I. pulley II. wedge III. wheel and axle IV. lever

II, III, and IV only

Which of the following statements best describes the data shown in the table provided?

Increasing the height of the inclined plane decreases the I.M.A. of the inclined plane.

The Smiths went out to cut down their Christmas tree for this year. Along with their truck, Mr. Smith brought his two sons and an axe. Why did Mr. Smith bring an axe with him?

The axe requires less effort to do the same work.

According to the law of conservation of energy, energy can neither be created nor destroyed. However, whenever energy is applied to a mechanical system, such as a machine, the useful amount of energy that is produced is always less than the initial amount of energy that was added to the system. Which of the following statements best explains this discrepancy?

The difference appears as heat.

Jim was clearing trash from his yard so that the construction crew could begin his pool. There was one large rock that needed to be moved. Why would it be easier for Jim if he used a lever and fulcrum?

The lever and fulcrum decrease the amount of force needed to move the rock.

Which of the following statements is true in any mechanical system?

The useful energy output is always less than the energy input.

According to the diagram, how does the amount of useful energy output compare with the amount of energy that was initially added to the system?

The useful energy output is less than 15% of the amount of energy that was initially added to the system.

Modern society depends heavily on gasoline powered engines, such as the one shown in the diagram below.

The useful energy output is less than 15% of the amount of energy that was initially added to the system.

Trevor is mowing his lawn with a push mower.Before lunch, he mows half of his lawn in 10 minutes. After lunch, he mows the remaining half in 15 minutes. With respect to the work done in pushing the mower,

Trevor's power was greater before lunch.

A knife is an example of what type of simple machine?

Wedge

Greg is moving a pile of dirt across his yard using a wheelbarrow. The main simple machines that make up the wheelbarrow are:

a lever and a wheel and axle.

The _______ of a machine is the amount by which a machine multiplies the force applied to it when accounting for energy lost due to friction.

actual mechanical advantage

A fish just bit the end of John's fishing line. To keep the fish from getting away, John wants to use more power to reel it in.

all of them

When a simple machine is used to perform a task, which of the following factors may be affected?

all of them

What does a pulley system need in order to reduce the force needed to lift an object?

at least one movable pulley

How does a simple pulley make it easier to lift an object?

by changing the direction of the input force

A wheelchair ramp is an example of what type of simple machine?

inclined plane

In each of these pictures, gears create a mechanical advantage. Which kind of simple machine do these gears represent?

wheel and axle

What type of simple machine is the knob of this water faucet?

wheel and axle

Tracy pushes a block up an inclined plane to a height of 1.0 m. If Tracy puts 505 J of work into the system, but only 444 J are used to elevate the block, what is the efficiency of the inclined plane?

88%

The diagram below shows the relationship among the amount of energy that is added to a mechanical system (Ein), the amount of useful energy that is produced by the system (Eout), and the amount of heat generated during the mechanical process.

*The amount of useful energy that is produced is less than the amount of energy that was initially added to the system. *The system obeys the law of conservation of energy.

In an experiment on motion, a cart weighing 240 N was pulled up an inclined plane. Which of the following would be the expected reading on the spring scale as the cart is pulled up an inclined plane set upon two books?

40 N

Newton's cradle is a science toy that is often used to demonstrate the law of conservation of energy.When one ball is raised, it acquires potential energy which is then transformed into kinetic energy once the ball is released.In theory, the total energy should be conserved such that the balls continue in perpetual motion. However, over time, the balls stop moving. Why?

Some of the energy is converted into heat.

Rick is moving a wheelbarrow full of bricks out to the curb. The bricks in the wheelbarrow weigh more than Rick is able to carry, yet he is able to move the bricks. How is this possible?

When Rick lifts the handles of the wheelbarrow most of the weight of the wheelbarrow's load goes onto its wheel.

A crowbar is an example of what type of simple machine?

lever

A pair of scissors is a compound machine. Which simple machines is a pair of scissors made up of?

lever and wedge

A tennis net post uses multiple simple machines to make raising and tightening the net easier. Based on the picture above, which simple machines does a tennis net post use?

pulley and wheel and axle

Carrie lifted a load using the lever shown above. Then, she lifted the load without using the lever.

the amount of energy needed to lift the load

The efficiency of a machine is defined as

the ratio of the work done by a machine (output) to the work required to use the machine (input).

There are eight stairs between Katie's English class and her physics class. Katie can run up these stairs at a constant speed.If Katie's mass is 45 kilograms and the total height of the stairs is 2 meters, what should be measured to determine how much power Katie uses while running up the stairs?

the time it takes her to run up the stairs

Reggie can do 50 push-ups in one minute. If the mass that Reggie is lifting with each push-up is measured at 92 kilograms, what must also be measured in order to determine his power output?

the vertical distance his body travels with each push-up

A bicycle is a compound machine. Which of the following parts of a bicycle fit the definition of a wheel and axle?

the wheels