Instructor Dr Tatiana Erukhimova Lectures 13 14 15 F Find F necessary to drag the box 1 at constant speed 1 2 Friction everywhere The advantage of a pulley What minimum force F is needed to lift the piano of mass M ID: 533860
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Slide1
Physics 218: Mechanics
Instructor: Dr. Tatiana Erukhimova
Lectures 13, 14, 15Slide2
F
Find F necessary to drag the box 1 at constant speed.
1
2
Friction everywhere. Slide3
The advantage of a pulley
What minimum force F is needed to lift the piano of mass M? Slide4
A faulty model rocket moves in the
xy
-plane (the positive
y
-direction is vertically upward). The rocket
’
s acceleration has components
a
x
(t)=
t2 and ay(
t)=-t, where =2.50 m/s4, =9.00 m/s2, and =1.40 m/s3. At t=0 the rocket is at the origin and has velocity with and Calculate the velocity and position vectors as functions of time. What is the maximum height reached by the rocket? What is the horizontal displacement of the rocket when it returns to y=0?Slide5
WORK (Chapter 7)Slide6
A person carries a bag of groceries of mass M with a constant velocity at the same height from the ground. Find the work done by a person on a bag. Slide7
A block of mass m starts at the top of an inclined plane. The coefficient of friction between the plane and the block is
. Assuming the block slides down the plane calculate the work done by each force.Slide8
First exam Tuesday, September 27, 7 – 8 pm
Sections 530, 531 105 HELD
Sections 532, 565
107 HELD
Section 566
109 HELDSlide9
All liquids, gels and aerosols must be in three-ounce or smaller containers.
No calculators and cell phones
BRING YOUR STUDENT ID!
Slide10
What is included?
Chapters 1-6
Kinematics, vectors, Newton’s lawsSlide11Slide12Slide13
KinematicsSlide14
In components:Slide15
If is given, you can find andSlide16
VectorsSlide17
Newton
’
s 2nd LawSlide18
Friendly advice
DO NOT…Slide19
DO NOT
use
Const acceleration
case formulas when acceleration is a function of time. You have to integrate or differentiate! What are the Const acceleration case formulas?Slide20
DO NOT
write the vector sign over a projection!Slide21
Q
DO NOT
forget
that
F
p
has two components:
F
p
cos θ and Fpsin θSlide22
Do Not Forget to
Write down what is given and express the answer in terms of what is given
Box the answer
Indicate the origin and positive
x
and
ySlide23
Problem 1 p. 122
A man pushes up on a 100 kg block with a force such that it drops from 2 meters to the ground at a constant velocity.
How much work is done by gravity?
What is the magnitude of the force he exerts?Slide24
Work Energy TheoremSlide25
A person is pulling a crate of mass M along the floor with a constant force F over a distance d. The coefficient of friction is
.
Find the work done by the force F on the crate.
Same if F changes as F
0
(1+x
2
/d
2
).
Find the work done by the force of friction on the crate (F is constant). Find the net work done on the crate if the crate is pulled with a constant velocity. Find the final velocity of the crate if the crate is pulled with a non-zero acceleration starting from the rest.
MSlide26
Have a great day!
Reading: Chapter 7