Download Newton`s Laws of Motion

NEWTON’S LAWS OF
MOTION
Force – The ability to cause a
change in a state of motion of an
object (Vector)
The only thing that can cause an
object to accelerate is a Force
An object at rest will remain at rest and an
object in motion will maintain a constant
velocity unless acted upon by a net external
force
Law of Inertia – The tendency of an object to
resist a change in motion
∑F = ma
For every action force there is an
equal and opposite reaction force
There is no such thing as a lone
force, all forces come in pairs
 3 people push on a boat that is 752 kg. The boat floats next
to a dock. Each of the people push on the boat with 80.5N
of force parallel to the dock.
(A) What is the acceleration of the boat if they all push in
the eastern direction?
(B) What is the magnitude and direction of the boat’s
acceleration if 2 of the people push in the west direction
and one of the people push toward the east?
Gilgur yells at his twins for the messy house.
The twins decide to pack their stuff on a
wagon and run away. The cart starts at rest
and pulls on the cart for 25m reaching a
speed of 6 m/s.
With what force did they pull on the wagon?
Velocity on
impact = 123
km/hr (34.2
m/s)
Time it takes to
come to a
complete stop:
2.6s
Mass: About
170 pounds
(77.1 kg)
Find Force
exerted on cliff
jumper?
 Gilgur is ice skating with his twins. After a while it’s
time to go home, but they don’t want to… So Gilgur
needs to start dragging his kids with a constant
horizontal force of 50N, the kids start to accelerate
at 1.3 m/s^2.
If his son has a mass of 22.6 kg, what is the mass of
the daughter?
 1) If Mr. Burns pulls on a .3kg pillow in opposite
directions with 10 N and his wife pulls on it with 11
N, what is the horizontal acceleration of the pillow?
Answer: 3.33 m/s^2
2) You are pulling your little sister on her sled.
When you exert a constant horizontal force of 110 N,
the sled has an acceleration of 2.5 m/s^2. If the sled
has a mass of 7 kg, what is the mass of your little
sister?
Answer: 37kg
A pitcher throws a 0.15kg baseball that gets
displaced 2m, accelerating it from rest to a
speed of about 90 mi/hr (40 m/s).
Estimate the force exerted by the pitcher on
the ball
 Two groups of canoeists meet in the middle of a
lake. A person in canoe 1 pushes on canoe 2 with a
force of 46 N to serperate the canoes. If the mass of
canoe 1 and its occupants is m1 = 150kg, and the
mass of canoe 2 and its occupants is m2 = 250kg.
(A) Find the acceleration the push gives to each
canoe.
(B) What is the separation of the canoes after 1.2s of
pushing?
 Mass – The measurement of how much matter is in an
object
 Weight – The measurement of how hard the force of gravity
is being exerted on an object
 What would happen to your mass & weight if you traveled
to different planets?
Jack and Jill lift upward on a 1.3kg pail of
water, with Jack exerting a force F1 of
magnitude 7 N and Jill exerting a force F2 of
magnitude 11N. Jill’s force is exerted at an
angle of 28 degrees with the vertical.
At what angle with respect to the vertical
should Jack exert his force if the pail is to
accelerate straight upward?
Two crewmen pull a boat through a lock. One
crewman pulls with a force of 130N at an
angle od 34 degrees. The second crewman, on
the opposite side of the lock, pulls at an angle
of 45 degrees.
With what force should the second crewman
pull so that the net force of the crewmen is the
forward direction?
You pull on a sled that has a mass of 4.6kg
with 6.2 N of force that is 35 degrees from
the horizontal.
How fast is it going after 1.5 seconds?
With what force do you need to pull on the
sled in order for it to come off the ground?
Normal Force - is the component,
perpendicular to the surface of contact, of
the contact force exerted on an object
**Misconception** - Normal Force is not
equal and opposite to weight
The fire alarm goes off and a 97 kg fireman
slides 3 meters down a pole to the ground
floor in 1.2 seconds.
What was the upward force exerted by the
pole on the fireman?
What is the upward force exerted by the
fireman if he just hangs on the pole?
 Charlie owns a shady donut business in an elevator. Charlie
sells donuts by the Newton. If the donuts have a mass of
0.8kg at what point in the elevator ride should you weigh
the donuts?
 (A) What is the weight of the donuts when the elevator
starts to go down with an acceleration of 2 m/s^2?
 (B) What is the weight of the donuts as the elevator is
traveling down with a constant speed of 5 m/s?
 (C) What is the weight of the donuts when the elevator
starts to go up with an acceleration of 2 m/s^2?
A jet can be
catapulted
from 0 to 155
mi/hr (51.4
m/s) in 2
seconds. If the
average force
exerted is
5.1 x 10^6 N
What is the
mass of the
jet?
 As part of a physics experiment, you stand on a
bathroom scale in an elevator. Though your normal
weight is 610 N, the scale at the moment reads 730N.
 (A) Is the acceleration of the elevator upward,
downward, or zero? Explain.
 (B) Calculate the magnitude of the elevator’s
acceleration?
A 23 kg suitcase is being pulled
by a handle that is an angle of 25
degrees above the horizontal. If
the normal force exerted on the
suitcase of 180 N, what is the force
applied to the handle?
 A 747 jetliner lands and begins to slow to a stop as
it moves along the runway. If its mass is 3.5 x 10^5
kg, its speed is 27 m/s. and the net braking force is
4.3 x 10^5 N. (A) What is its speed 7.5s later? (B)
How far has it traveled in this time?
 A 6kg block of ice is acted on by two forces F1 and
F2 as shown in the diagram. If the magnitude of F1
= 13N and F2 = 11N, find (A) the acceleration of the
ice and (B) The normal force exerted on it by the
table.
 A 873 kg dragster, starting from rest, attains a speed of 26.3
m/s in 0.59s.
 What is the magnitude of the force on the dragster during
this time?
 A block of ice is pushed with a force of 40N at an angle of
25 degrees below the horizontal. The block of ice has a
mass of 12kg.
 What is the normal force on the ice block?
 With what acceleration will the ice block have?