Question

6. If a large force is exerted on an object, when is no work performed?
a
when the object moves
b
when the object does not move
c
when there is no friction
d
when the power is too large


7. Adam lifts a book from the floor, carries it across the room, and places it on a high shelf. When is Adam doing work on the book?

Work = Force x Distance
a
He does work only while he carries the book across the room.
b
He does work from the moment he touches the book until he lets it go.
c
He does work as he picks up the book and as he lifts it to the shelf.
d
He does work on the book at no time during this process.


8. Which of the following are examples of work being done on an object? Choose the 4 that apply.

a
lifting a rock off the ground
b
holding a 50 kg barbell over your head
c
carrying a box up a flight of stairs.
d
pushing a grocery cart through the store
e
lifting a bag of groceries
f
pushing on a car that will not move
g
wind blowing against a tree


9. What can a car manufacturer do to increase the mechanical advantage of a steering wheel?

a
increase the radius of the steering wheel
b
shorten the axle length of the steering wheel
c
lengthen the axle length of the steering wheel
d
decrease the radius of the steering wheel


10. Find the efficiency of a machine that does 900 J of work if the input work is 1,200 J. You must show all your work.
Efficiency = Output work/Input work x 100%

Answer 1

Here are the answers to your questions:

**6. If a large force is exerted on an object, when is no work performed?**
**b** when the object does not move
*Explanation*: Work is defined as force applied over a distance. If there is no movement (distance = 0), then no work is done, regardless of the size of the force.

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**7. Adam lifts a book from the floor, carries it across the room, and places it on a high shelf. When is Adam doing work on the book?**
**c** He does work as he picks up the book and as he lifts it to the shelf.
*Explanation*: Work is done when there is a force applied in the direction of the movement. Adam does work when he lifts (work against gravity) and when he positions the book on the shelf.

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**8. Which of the following are examples of work being done on an object? Choose the 4 that apply.**

a) lifting a rock off the ground
c) carrying a box up a flight of stairs
d) pushing a grocery cart through the store
e) lifting a bag of groceries

*Explanation*: Work is done when a force causes an object to move in the direction of the force. Holding a weight does not involve movement; therefore, option b) (holding a 50 kg barbell over your head) and option f) (pushing on a car that will not move) do not qualify. Additionally, g) (wind blowing against a tree) does not constitute work being done on the tree.

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**9. What can a car manufacturer do to increase the mechanical advantage of a steering wheel?**
**a** increase the radius of the steering wheel
*Explanation*: Increasing the radius of the steering wheel allows for a larger torque to be applied with less effort, resulting in increased mechanical advantage.

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**10. Find the efficiency of a machine that does 900 J of work if the input work is 1,200 J.**
To find the efficiency, we use the formula:

\[
\text{Efficiency} = \left( \frac{\text{Output Work}}{\text{Input Work}} \right) \times 100\%
\]

Substituting in the values:

\[
\text{Efficiency} = \left( \frac{900 \, \text{J}}{1200 \, \text{J}} \right) \times 100\%
\]

Calculating the fraction:

\[
\text{Efficiency} = (0.75) \times 100\% = 75\%
\]

So, the efficiency of the machine is **75%**.