Physical Science~ Chapter 14 Hw Questions

How can two machines appear identical and yet not have the same actual mechanical advantage?

One can have more friction than the other

Why can no machine be 100% efficient?

Some of the energy input will always be used to overcome the force of gravity and the effects of friction and air resistance.

You test a machine and find that it exerts a force of 5 N for each 1 N of force you exert operating the machine. What is the actual mechanical advantage of the machine?

5

How does the work done on a machine compare to the work done by a machine?

Because of friction, the work done by a machine is always less than the work done on the machine.

Why is the actual mechanical advantage of a machine always less than its ideal mechanical advantage?

Because of friction, the work done by a machine is always less than the work done on the machine. Because friction is always present, the actual mechanical advantage of a machine is always less than the ideal mechanical advantage.

A machine produces a larger force than you exert to operate the machine. How does the input distance of the machine compare to its output distance?

Because the output force is greater than the input force, the input distance must be greater than the output distance.

How can you increase the work output of a machine?

Increase the work input to the machine, or reduce any friction that limits work output.

You do 200 J of work pulling the oars of a rowboat. What can you say about the amount of work the oars do to move the boat? Explain.

Less than the 200 J of work are done to move the boat because some of the input work is lost to friction forces.

How can using a machine make a task easier to perform?

Machines make work easier to do by altering the size of force needed, the direction of a force, or the distance over which a force acts.

How much work is done when a vertical force acts on an object moving horizontally?

None

What information would you use to calculate the efficiency of a machine?

Output \ input x 100

What formula relates work and power?

Power = work / time

You lift a large bag of flour from the floor to a one meter high counter, doing 100 joules of work in 2 seconds. How much power do you use to lift the bag of flour?

Power= 50 W

What changes can a machine make to a force?

Size of force; direction of force; distance through which a force acts.

What conditions must exist in order for a force to do work on an object?

Some of the force must act in the same direction as the object moves.

How much work does a 25 Newton force do to lift a potted plant from the floor to a shelf 1.5 meters high?

Work= 37.5 J