The first exam will be on Tuesday, September 25, room 109 in Heldenfels building. Section 807 and...
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Transcript of The first exam will be on Tuesday, September 25, room 109 in Heldenfels building. Section 807 and...
The first exam will be on Tuesday, September 25, room 109 in Heldenfels building.
Section 807 and half of the Section 808 (students with last name starting with A to H) will have exam from 7 to 8 pm.
Students from Section 808 with last name starting with J to Z, and all students from Section 809, will have exam from 8:15 pm to 9:15 pm.
Students that have the exam from 7 to 8 pm will not be allowed to leave earlier than 8 pm.
No calculators and cell phones in the room during the test.
Don’t use your own scratch paper; there will be plenty of it in the room.
Please DO NOT FORGET TO BRING YOUR STUDENT ID!
Ch. 6 Quiz
A block of mass M is pushed against a vertical surface. The coefficient of friction between the surface and the block is equal to . If angle is known, what is the minimum magnitude of P to hold the block still?
P
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?
)0()0(2
1)( 2 xtvtatx c
)0()( vtatv c
))()((2)()( 1212
22 txtxatvtv c
Do Not Forget to
•Write down what is given and express the answer in terms of what is given
•Box the answer
A Recipe for Solving Second Law Problems1. Sketch Isolate the body (only external forces but not forces
that one part of the object exert on another part)
2. Write down 2nd Newton’s law
amF
Choose a coordinate system Write 2nd Newton’s law in component form:
yyxx
yxyx
maFmaF
jmaimajFiFF
,
3. Solve for acceleration
Pulling Against FrictionA sled of mass m is on a surface with coefficients of kinetic
friction and static friction s. You pull with a constant force F at an angle The sled does not leave the surface and moves to the right.
1. What is a minimum force needed to bring the sled in motion?2. What is the magnitude of the acceleration? 3. What angle maximizes the acceleration?
Friction
Two types of friction:1. Kinetic: The friction force
that slows things down2. Static: The force that
makes it hard to even get things moving
Kinetic Friction
• For kinetic friction, it turns out that the larger the Normal Force the larger the friction. We can write
FFriction = KineticFNormal
Here is a constant• Warning:
– THIS IS NOT A VECTOR EQUATION!
Static Friction• This is more complicated• For static friction, the friction force can vary
FFriction StaticFNormal
Example of the sled: – If I don’t push, what is the static friction
force?– What if I push a little?
Box on an inclined planeA box with mass m is placed on a frictionless incline
with angle and is allowed to slide down.
a) What is the normal force?
b) What is the acceleration of the box?