Check
Your Understanding
Express your understanding of the concept and mathematics
of work by answering the following questions. When done,
click the button to view the answers.
1. Apply the work equation to determine the amount of
work done by the applied force in each of the three
situations described below.
2. On many occasions, there is more than one force acting
upon an object. A
free-body
diagram is a diagram that depicts the type and the
direction of all the forces acting upon an object. The
following descriptions and their accompanying free-body
diagrams show the forces acting upon an object. For each
case, indicate which force(s) are doing work upon the
object. Then calculate the work done by these forces.
|
Free-Body
Diagram
|
Forces Doing
Work
on the
Object
|
Amount of Work
Done
by Each
Force
|
A 10-N force is applied to push a block
across a friction free surface for a displacement
of 5.0 m to the right.
|
|
|
A 10-N frictional force slows a moving
block to a stop after a displacement of 5.0 m to
the right.
|
|
|
A 10-N force is applied to push a block
across a frictional surface at constant speed for a
displacement of 5.0 m to the right.
|
|
|
An approximately 2-kg object is sliding at
constant speed across a friction free surface for a
displacement of 5 m to the right.
|
|
|
An approximately 2-kg object is pulled
upward at constant speed by a 20-N force for a
vertical displacement of 5 m.
|
|
|
3. Before beginning its initial descent, a roller coaster
car is always pulled up the first hill to a high initial
height. Work is done on the car (usually by a chain) to
achieve this initial height. A coaster designer is
considering three different incline angles at which to drag
the 2000-kg car train to the top of the 60-meter high hill.
In each case, the force applied to the car will be applied
parallel to the hill. Her critical question is:
which
angle would require the most work? Analyze the data,
determine the work done in each case, and answer this
critical question.
|
Angle
|
Force
|
Distance
|
Work
(J)
|
a.
|
35 deg
|
1.12 x 104 N
|
105 m
|
|
b.
|
45 deg
|
1.39 x 104 N
|
84.9 m
|
|
c.
|
55 deg
|
1.61 x 104 N
|
73.2 m
|
|
4. Ben Travlun carries a 200-N suitcase up three flights
of stairs (a height of 10.0 m) and then pushes it with a
horizontal force of 50.0 N at a constant speed of 0.5 m/s
for a horizontal distance of 35.0 meters. How much work does
Ben do on his suitcase during this
entire motion?
5. A force of 50 N acts on the block at the angle shown
in the diagram. The block moves a horizontal distance of 3.0
m. How much work is done by the applied force?
6. How much work is done by an applied force to lift a
15-Newton block 3.0 meters vertically at a constant
speed?
7. A student with a mass of 80.0 kg runs up three flights
of stairs in 12.0 sec. The student has gone a vertical
distance of 8.0 m. Determine the amount of work done by the
student to elevate his body to this height. Assume that her
speed is constant.
| 8. Calculate the work done by a 2.0-N force
(directed at a 30° angle to the vertical) to
move a 500 gram box a horizontal distance of 400 cm
across a rough floor at a constant speed of 0.5
m/s. (HINT: Be cautious with the units.) |
|
9. A tired squirrel (mass of 1 kg) does push-ups by
applying a force to elevate its center-of-mass by 5 cm.
Estimate the number of push-ups that a tired squirrel must
do in order to do a approximately 5.0 Joules of work.
Thank : http://www.physicsclassroom.com/Class/energy/u5l1aa.cfm
