Transcript 4.1 Worksheet

Chapter 4.1
Review
1. What is the
difference in a field
force and a contact
force? Give one
example of each.
Field forces do not
require contact,
gravity.
Contact forces
require contact,
friction.
2. Draw a free body
diagram of a book on
a table being pushed
at a constant velocity.
Ff and FP are equal in magnitude, mg
and FN are also equal in magnitude.
The net force on the book is zero, so
it is in equilibrium.
3. Draw a free
body diagram of
a baseball being
hit by a bat.
The bat is applying a force FB and gravity
is pulling downward mg. The forces are
NOT balanced so the ball is NOT in
equilibrium. It is accelerating.
4. Draw a free
body diagram of
a box sitting on
an incline.
Since the box is
not moving, it is
not accelerating.
The net force on
the box must be
zero, so these
three forces must
balance each
other. The box is
in equilibrium.
5. Draw a free body
diagram of a box
sliding down an
incline at a constant
speed.
Even though the
box is moving, it is
not accelerating
because the speed
is constant.
The box is in
equilibrium, so the
free body diagram
is the same as in
the previous
question.
6. What is the minimum
number of forces
(besides zero) that can
be applied to an object
in equilibrium?
Two. The forces
must be equal
and opposite.
7. A cat runs at a
constant velocity,
10 m/s north. What is
the net force on the
cat?
Zero. At a constant
velocity, there is no
acceleration. No
acceleration means
no net force.
8. A ball is falling through
the air at a constant speed
of 35 m/s. If the weight of
the ball is 5 Newtons,
what is the force of air
resistance on the ball?
5 Newtons. Since the
object is falling at a
constant velocity, it is not
accelerating. The forces
must be balanced, so air
resistance must equal
gravity.
9. Dalyn is pushing
upfield with a force of
200 N. If a linebacker
hits him from the left
with a force of 150 N,
what is the net force
on Dalyn?
2
200
2
150
2
c
+
=
c = 250 N
tanq = 150/200
37° to the right of
upfield
10. With what force
would Charles have to
hit Dalyn to hold
Dalyn at a constant
velocity in question 9?
(Better grammar!)
Constant velocity means all
the forces must be balanced.
Charles must apply an equal
force in the opposite direction
(this is called an equilibrant
force), 250 N, 37° left of back
downfield.