Download Newton`s 1st and 2nd law review packet: Read Ch 4 and 5 sections

Newton’s 1st and 2nd law review packet:
Read Ch 4 and 5 sections that have been assigned for HW so far
Review your HW problems and packets and worksheets: all solutions are posted
Watch Dan Fullerton videos on 1st law, 2nd law, friction, freebody diagrams.
This review packet is all word problems. There is more content on the test besides word problems:




Understand the 1st law and be able to recognize and give examples of how the 1st law is involved
in certain situations
Understand inertia, mass and weight
Be able to draw and interpret free body diagrams
Be able to identify a variety of different forces including the special type of force known as
normal force
How to solve Newton’s 2nd law word problems:
the best way is to do it just like SWAG




draw a sketch with all the info
list the knowns ex: a box is pushed to the right with a force of 60 N, Fpush = 60 N
list the unknowns and what are you solving for?
Draw a free body diagram of the object
examples of forces that might be included:
Force of earth on object….weight (Fg),
Force of hand, rope, engine, etc on object…..Fapplied,
Force of air, water, etc on object…F drag
Force of surface on object…Ffriction
Support force of surface on object…normal force, F N

Make sure you have mass and weight calculated for the object
o Mass in kilograms
o Weight in Newtons weight = Fg = mass x accel due to gravity = m g

Look at the free body diagram and figure out Fnet
o Fnet = sum of all forces in the diagram causing accel
o First write it in words, then re-write it as variables and number values

Write out the Fnet = ma equation
o First in words, then with variables and numbers

Remind yourself what you are solving for and solve the equations

REALITY CHECK:
 correct sign according to your sketch and FBD? Reasonable number?
1.A crate is pushed to the left with 20 N and also pulled to the left with 12 N . There is 25 N of
friction. What is the size and direction of the net force?
2. Calculate the acceleration of a 35 kg mass that has 270 N of net force applied horizontally.
3. What is the mass of an object that can be accelerated horizontally at 4.4 m/s2 by a force of
450 N?
4. On earth you have a weight of 550N. In an elevator that accelerates upward, your ‘weight’
temporarily becomes 590 N. When slowing down, your ‘weight’ temporarily becomes 510 N.
a. what is your mass?
b. what is the acceleration while you speed upwards?
c. what is the acceleration while it is slowing down?
5. The rope that is holding up a large pipe snaps and the pipe is falling. If the pipe has a mass
of 1100 kg, what is its acceleration as it falls?
6. What is the tension in a rope being to hold a 200 kg crate at rest?
To raise it at a constant velocity?
To lower it at a constant velocity?
To accelerate it upward at 1.2 m/s2?
7. A tow truck is trying to drag your car out of a snowbank. Car’s mass is 2000 kg. The truck is
able to apply 1500 N of force to accelerate you at 0.1 m/s2 out of the snow.
Draw a FBD.
Calculate the force of the snow on your car.
8. You are skydiving. Air drag is included. The plane takes you up 3000 m. You step out of the
plane and start falling. You fall for about 10 seconds before you reach terminal velocity. Then
you fall for 45 seconds more and then your parachute opens.
To the side of each FBD, draw the direction of velocity, Fnet and accel.
a. draw a fbd for the moment you are out of the plane but you really haven’t started
falling much.
b. draw a fbd at terminal velocity.
c. draw a fbd with the parachute opened.
9. A rocket engine exerts a force of 2 x 107 N at liftoff. The rocket weighs 25 x 106 .
a. what is the mass of the rocket?
b. draw a FBD.
c. what is the net force on the rocket?
d. what is the acceleration of the rocket?
e. what happens after the engine is out of fuel?
The following questions are about a couple of furniture movers. They are trying to move a
heavy couch by sliding it across a carpet. The mass of the couch is 150 kg. The coefficient of
static friction is 0.6 and of kinetic friction is 0.55.
10. What happens to the amount of static friction force as they gradually push on the couch>?
Draw a FBD to help explain.
11. When the couch is still not moving, what is true about the amount of push compared to the
amount of static friction? Draw an FBD to help.
12. Calculate the maximum push necessary to get it moving.
13. What is the maximum amount of static friction?
14. If they apply 600 N of force, will it move or not? How do you know?
15. Calculate the amount of kinetic friction present once they get it moving.
16. How hard do they have to push to keep it moving at a constant velocity?
17. If they push with 900 N of force, will the couch move? Accelerate? How do you know?
18. If yes, calculate the acceleration.
19. They drag it across a different area of the carpet and notice that it takes 1029 N of force to
keep it moving at a constant velocity. Calculate the coefficient of friction. Is it static or kinetic?