Work and Machines

Final Review

• Nancy pushed a box with a force of 45 N for 15m. How much work did Nancy do?

Answer

• 675J

• The force that you apply to a machine is the?

Answer

• Input Force

• When casting a fishing pole you need to apply 10N of force. The pole in return will put out 30N of force. Calculate the mechanical advantage of the fishing pole?

Answer

• 30N/10N= 3

• The mechanical advantage of a machine is the number of times a machine increases…

Answer

• The force exerted on the machines

• What is the ideal mechanical advantage of an incline plane that is 6.0 m long and 1.5 m high?

Answer

• 6.0/1.5= 4.0

• An ideal machine would have an efficiency of what?

Answer

• 100%

• The ideal mechanical advantage for an inclined plane is equal to the length of the inclined plane divided by the what?

Answer

• Height

• Pulling down on a rope to hoist a sail on a sailboat is an example of a machine that does what?

Answer

• Changes the direction over which a force is exerted.

• The ideal mechanical advantage of a wheel and axle is equal to the…

Answer

• Radius of the wheel divided by radius of axle

• If tight, rusty scissors have an efficiency of 50 %, half of your work is wasted do to what?

Answer

• Friction

• What is the formula used to calculate the efficiency of a machine.

Answer

• Output work/inputwork x 100%

• A ramp is an example of a simple machine called what?

Answer

• Inclined plane

• Which of these is an example of a third-class lever?

Answer

• Your elbow

• If the radius of a doorknob is 6.0 cm and the radius of its inner rob is 2.0 cm, what is the mechanical advantage?

Answer

• 6.0/2.0=3

• A machine that utilizes two or more simple machines is called a what?

Answer

• Compound Machine

• You do 5,000 J of work using a sledge hammer. The sledge hammer does 2,000J of work on the spike. What is the efficiency if the sledge hammer?

Answer

• 40%

• One example of a compound machine is a?

Answer

• Bike, car, any thing that uses a variety of simple machines.

• Which of the following describes a first class lever?

Answer

• -----------/\--------------– Fulcrum is in the middle

• A(n)_________ is a grooved wheel with a rope, chain or cable running along the groove.

Answer

• Pulley

• Which of the following simple machines is an inclined plan wrapped around a post?

Answer

• Screw

• If you exert a force of 20 newtons to push a desk 10 m, how much work do you do on the desk?

Answer

• 200J

• If a pulley is attached to something that doesn’t move, is called what?

Answer

• Fixed pulley

• The fixed point that a lever pivots around is called the

Answer

• Fulcrum

• A machine can do any of the following except…..

Answer

• Increase work

• How does a ramp make it easier to move a heavy object a certain distance?

Answer

• It decreases the amount of force required to move the object.

• When you raise or lower a flag on a flagpole, you are using a (n)

Answer

• Pulley

• What do machines do?

Answer

• Change amount of force you exert or the distance over which you exert the force.

• Which of the following equations should be used to calculate work done?

Answer

• W=FxD

• Power is measured in units called

Answer

• Watts

• The power of a light bulb that converts electrical energy at a rate of 100J per second is what?

Answer

• 100 Watts

• ______ is the rate at which work is done.

Answer

• Power

• If you apply a force of 10N to a box and push it 10 m in 10 s, how much power did you deliver?

Answer

• 10 Watts

• For work to be done on an object…

Answer

• Object must move in the same direction as the force applied

• Which of these is an example of work being done on an object.

Answer

• Pushing an object across the room

• Work is measured in what?

Answer

• Joules

• If you exert a force of 15 N to push a desk 20 m, how much work do you do on the desk?

Answer

• 300J

• ________ is the rate at which work is done.

Answer

• Power