Test: machines (Part 2)

Question 1

Humans can do more work with machines than without them.

Answer 1

True

Question 2

Which of the following statements correctly identifies the relationship between kinetic and static friction?

Answer 2

Kinetic friction occurs when an object moves, while static friction keeps an object from moving.

Question 3

Friction is always undesirable.

Answer 3

False

Question 4

All machines are less than 100% efficient.

Answer 4

True

Question 5

The mechanical advantage of an inclined plane increases with the length of the ramp, assuming the height is constant.

Answer 5

True

Question 6

The screw has a very low mechanical advantage.

Answer 6

False

Question 7

A first-class lever is an almost perfectly efficient machine.

Answer 7

True

Question 8

Use the information given on the diagram to complete the calculations.
F i = 600 N
F o = 1,200 N
Heights = 4 m
Slope = 12 m

Answer 8

The IMA = 2

1,200/600=2

The AMA = 3

12/4=3

The efficiency = 67%

2/3=0.667 or 0.67

Question 9

An automobile steering wheel is shown. The ideal mechanical advantage of this wheel and axle = .
Ra = 2 cm
Rw = 18 cm

Answer 9

18/2=9

The IMA is 9

Question 10

Any time energy is converted from one form to another some unusable _____ is _____ .

Answer 10

Energy
Lost

Question 11

Friction between sliding surfaces is dependent upon the _____ force.

Answer 11

Normal

Question 12

The coefficient of kinetic friction for copper is . (Your answer should be given to the nearest thousandths.)
Copper is 40 lbs
The pulley pulls at 1.5 lbs

Answer 12

The coefficient of kinetic friction for copper is 0.038.
1.5/40=0.0375 or 0.038
This coefficient does apply to all similar copper surfaces.

Question 13

The ratio between the force of friction and the normal force is the _____ of friction.

Answer 13

Coefficient

Question 14

A force of 20 N is executed to raise a rock weighing 30 N. The actual mechanical advantage is .

Answer 14

30/20=1.5
1.5

Question 15

A movable single pulley _____ the required effort.

Answer 15

Decreases

Question 16

In a real pulley system, the work supplied must be _____ the work accomplished.

Answer 16

Greater than

Question 17

The efficiency of the wedge is low because of _____ .

Answer 17

Friction

Question 18

Choose the smallest rope that would be able to pull the 8,000 Newton (N) pallet across a warehouse floor at a constant rate.

Answer 18

rope with a maximum force of 4,000 N

Question 19

On sliding surfaces, friction acts _____.

Answer 19

parallel

Question 20

In an actual lever system, Fo × do represents _____.

Answer 20

work output

Question 21

Why is the applied effort only ½ of the weight to be lifted in the movable single pulley system?

Answer 21

The fixed hook carries ½ the weight

Question 22

A wheel and axle system with the highest mechanical advantage has _____.

Answer 22

a large wheel and a small axle