Kinematics - Mr. Schroeder

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Nov 14, 2013 (3 years and 9 months ago)

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Physics 20 Unit
2: Dynamics

1

Physics 20
-

STA

Work Booklet


Unit I


Dynamics

Chapter
3



Forces









Name: ______________________________________________________________________________


Physics 20 Unit
2: Dynamics

2




Physics 20 Unit
2: Dynamics

3




3.1


The Nature of Force


1.




2.

Shana, Kelsey, and Amanda pull on a toy exerting forces described in the diagram below. Let North
be positive and south Negative. Determine the net force acting on the toy.









3.

Three forces act on an object. Two are pulling to the south, one
with a magnitude of 35N and the other
with a
magnitude

of 23N. The third force is pulling towards the north with a magnitude of 29N.
Determine the net force acting on the object.




Physics 20 Unit
2: Dynamics

4

4.

Two forces pull on an object. One force pulls with 30N to the west. The second force is unknown.
Determine the unknown force if the net force is 40 N to the East?











5.

A car
is speeding up
. The weight of the car is 12 000 N [down]. The force o
f air resistance is 3600 N
[backward]. With the engine engaged, the
engine applies a

20 000

N [forward]

force to the axels
. Draw a
free
-
body diagram for this situation.











6.

Two people, A and B, are dragging a canoe out of a
lake onto a beach using light ropes. Each person
applies a force of 60.0 N [forward] on the rope. The
force of friction exerted by the beach on the canoe is
85.0 N [backward]. Starting with a free
-
body
di
agram, calculate the net force on the canoe.











7.

Two dogs, A and B, are pulling a sled across a horizontal, snowy

surface. Dog A exerts a force of

200
N [forward] and dog B a force

of 150 N [forward]. The force of

friction exerted by the snow on

the sled is
60 N [backward]. The

driver attempts to slow down the

sled by pulling on it with a force

of 100 N
[backward]. Starting with

a free
-
body diagram, calculate the

net force on the sled.











Physics 20 Unit
2: Dynamics

5


8.

In a tractor pull, four tractors are

connected
by strong chains to a

heavy load. The load is initially

at
rest. Tractors A and B pull with

forces of 5000 N [E] and 4000 N [E]

respectively. Tractors C and D pull

with forces of 4500 N [W] and

3500 N [W] respectively. The

magnitude of the force of frictio
n

exerted
by the ground on the load

is 1000 N.


(a) Starting with a free
-
body

diagram, calculate the net force

on the load.

(b) If the load is initially at rest,

will it start moving? Explain.














9.

The total weight of a biker and her

motorbike is 1800 N [down].
The engine applies a force of

500 N

[forward]. The air resistance

and friction

acting on the

biker and bike is 200 N [backward]. The

normal
force exerted by the road on the

biker and bike is 1800 N [up].

(a) Consider the biker
and bike as a single

object. Draw a free
-
body diagram for

this object.

(b) Calculate the net force.


























Answers

1)

FBD


2)

140N [North]

3)

29N [South]


4)

70N [East]


5)

FBD

6)

35.0N

7)

190N [forward]

8)

a)

0N
b)

No, not moving.

9) a)

FBD
b)

300N [forward]

Physics 20 Unit
2: Dynamics

6

3.2


Newton’s First and Second Law


1.

Use Newton’s first law to explain why

(a) steel barriers usually separate the cab of a truck from the

load

(b) trucks carrying tall loads navigate corners slowly, and

(c) customers

who order take
-
out drinks are provided with lids.
















2.

Give two examples
that illustrate the property of
inertia for

both a stationary and a moving object.
















3.

Use Newton’s first law to describe the

motion of


(a) a

car that attempts to go around an icy

curve too quickly

(b) a lacrosse ball after leaving the

lacrosse stick.












Physics 20 Unit
2: Dynamics

7

4.

Apply Newton’s first law and the concept

of inertia to each of these situations.

a)

How could you remove the newspaper

without
toppling the plastic beaker?




b)

While moving at constant speed on a

level, snowy surface, a snowmobiler

throws a ball vertically
upward. If the

snowmobile continues moving at

constant velocity, the ball returns to

the driver.
Why does the ball land

ahead
of the driver if the snowmobile

stops? Assume that the air
resistance

acting on the ball is negligible.










5.

Determine the accelerations which result when a 12
-
N net force is applied to a 3
-
kg object and then to
a 6
-
kg object.








6.

A net force of 15

N is exerted on an encyclopedia to cause it to accelerate at a rate of 5 m/s
2
.
Determine the mass of the encyclopedia.







7.

Suppose that a sled is accelerating at a rate of 2 m/s
2
. If the net force is tripled and the mass is
doubled, then what is the ne
w acceleration of the sled?









Physics 20 Unit
2: Dynamics

8


8.

A lacrosse player exerts an average

net horizontal force of 2.8 N

[forward] on a 0.14
-
kg lacrosse

ball
while running with it in the

net of his stick. Calculate the average horizontal

acceleration of the ball
while in

contact with the lacrosse net.






9.

The net force acting on a 6.0
-
kg grocery cart is 12 N [left]. Calculate

the acceleration of the cart.












10.

A net force of 34 N [forward] acts

on a curling stone causing it to

accelerate at 1.8 m/s2 [forward] on

a

frictionless icy surface. Calculate

the mass of the curling stone.


















Answers

1)

Answers Vary

2)

Answers Vary

3)

Answers Vary

4)

Answers Vary

5)

a=4

m/s
2

and a=2

m/s
2

6)

3kg


7)

3m/s
2

8
)
20 m/s
2

9)
2.0 m/s
2



10
)

19 kg

Physics 20 Unit
2: Dynamics

9


3.3


Multi
Force Analysis


1.

Two forces act on an object. The first force pulls 400N to the East while the second pulls 600 N to
the West. The object accelerates 5.00 m/s
2

to the West. Determine the mass of the object.









2.

A ball has a mass of 0.240 kg and is thrown straight up into the air, the initial acceleration of the ball
is 2.69 m/s
2
. What is the applied force on the ball?










3.

Bryce applies a horizontal force of 120 N to the East on her 10.0kg toboggan causing it

to accelerate
2.00 m/s
2

to the East. Determine the force of friction opposing the toboggan’s motion.










4.

Three forces act simultaneously on an

object:
F
1

is 65 N [30.0
°
],
F
2

is 80 N [115
°
],

and
F
3

is 105 N
[235
°
]. Calculate the net

force

and direction

acting on the object.

















Physics 20 Unit
2: Dynamics

10

5.

While in the water, a force of 320 N [up] exerted by the water on a dolphin causes the dolphin to
jump up. The acceleration of the dolphin is 2.6 m/s
2

[up].

a) Calculate the mass of the dolphin.

b) What

would be the acceleration of the dolphin if it had the same strength but half the mass?


























6.

Two people, A and B, are dragging a sled on a horizontal, icy surface

with two light ropes. Person A
applies a force of 65.0 N [30.0
°
] on one
rope. Person B applies a force of 70.0 N [300
°
] on the other
rope. The force of friction on the sled is negligible and the ropes

are parallel to the icy surface.
Calculate the net force on the sled.






















Physics 20 Unit
2: Dynamics

11

7.

An ice hut used for winter fishing
is resting on a level patch of snow. The combined mass of the hut
and angler inside is 80 kg. A wind exerts a horizontal force of 205 N on the hut, and causes it to
accelerate. While in motion, the magnitude of the force of friction acting on the hut is 19
6 N. What is
the acceleration of the hut?



















8.

A 25
.0
-
kg store sign is suspended

as shown in Figure 3.18.

Calculate the forces
F
T1

and
F
T2

exerted at
the point at which

the sign is suspended.


















Answers

1)

40.0kg

2)

3.00 N

3)

100N

4)

42N [27° E of S] or [63° S of E]

5)

a=5.2m/s
2

6)

95.5N [17.1° S of E] or [72.9° E of S]

7)

0.12 m/s
2

(forward)

8
) FT
1
=
299N [125°] and FT
2
=172N [0°]



Physics 20 Unit
2: Dynamics

12

3.
4

Force of Friction




1.

A 2.6 kg sled is pulled along a horizontal surface at a constant velocity to the south. If the
coefficient

of kinetic friction between the surface
s

is 0.17, determine the force of friction acting
on the sled?






















2.

Due to a frictional force

of 3.30 N, a 20 kg curling rock slides to rest along a horizontal sheet of
ice. Calculate the coefficient of kinetic friction between the curling rock and the ice.







Physics 20 Unit
2: Dynamics

13

3.

The coefficient of static friction can be calculated knowing the foce applied at the

threshold of
motion. (i.e.) just as the object beging to move. A 220 g block is placed on a horizontal surface.
If a force of 1.2 N is applied and just starts the object in motion, determine the coefficient of
static friction between the two objects. [
0.56]












4.

A larger force is required to start an object moving than is needed to keep the object moving. A
250 g glass block is set on a glass plate and a horizontal force is applied. The force is gradually
increased in magnitude. When the applied force reaches a

value of 2.3 N the block starts to
move. The force required to keep the block moving at constant velocity is 0.98 N. Deteremine
the
coefficient

of :

a)

Static friction between the block and the surface [0.94]

b)

Kinetic Friction between the block and the surf
ace [0.40]














5.

The driver of a 2600 kg truck travelling at 13.1 m/s along a level, but icy road steps on the brakes.
The wheels lock and the tires skid along the icy surface for a distance of 26.2 m before coming to
a stop. Calculate the coeffic
ient of kinetic friction between the tires’ surface and the ice [0.33]











Physics 20 Unit
2: Dynamics

14



6.

A 100N force is applied to accelerate a 20 kg box along a horizontal sidewalk where the kinetic
coefficient of friction between the box and sidewalk is 0.40. Determine the
magnitude of the
box’s acceleration.












7.

A force of 31 N [forward] is needed to

start an 8.0
-
kg steel slider moving along

a horizontal steel
rail. What is the

coefficient of static friction?














8.

A biker and his motorcycle have a weight

of
2350 N [down]. Calculate the force of

kinetic
friction for the rubber tires and dry

concrete

(u=0.70
)
if

the motorcycle skids.















Answers

1)

4.3N


2)

0.017N


3)

0.56

4)

a) 0.94

b) 0.40

5)

0.33


6)

1.1 m/s
2



7)

0.40


8
)
1.6 X 10
3

N