# wk4-PPT

```Announcements
Tutoring through the Physics Department is available according to the schedule below
TA: Phil Lo, pyl3@njit.edu
FRIDAYS 11:30-2:30pm ROOM 409 Tiernan
MONDAYS 2:30-5:30pm Room 409 Tiernan EXCEPT weeks that we have common exams.
For the weeks that we have common exams, instead of Monday (when we have the exam),
tutoring will be available the Saturday BEFORE the exam from noon-3pm, also in Room
409Tiernan.
Mondays Noon-2pm and Thursdays 10AM-1pm in Tiernan 401
Common Exam 1 WILL NOT INCLUDE todays material
• Common Exam will be 18 multiple choice questions.
• Equation sheet is posted on web page
• Practice exams are be posted on web page
1
Common Forces
Fundamentally, N, f, T forces are electromagnetic forces
Riding in an accelerating vehicle
In frame of reference of car, person moves
due to ‘ficticious’ force
Fictitious Force
Earth is Reference
Car is Reference
Iclicker Question #1
Which of the following statements is correct:
(1) It is possible to have motion in the absence of forces on an object
(2) It is possible to have forces on an object in the absence of motion
of the object
A)
B)
C)
D)
Only statement (1) is correct
Only statement (2) is correct
Both statements are correct
Neither statement is correct
Iclicker Question #2
A frictionless hockey puck has two forces acting on it as shown in the
diagram. The magnitude of both forces is 10 Newtons. For a 0.5 kg
puck, what is the puck’s acceleration in the y direction?
A)
B)
C)
D)
E)
zero
+ 28 m/s2
- 28 m/s2
+14 m/s2
Can not answer since it depends
on the motion in the x direction
y
F

x

F
Fan powered sail – Does this violate
Newton’s Third law?
http://www.lghs.net/ourpages/users/dburns/RRPhysics/Roa
d_Runner_Physics/Movie_files/FanPoweredSail.mov
Is the fan in this one OK? How about the
balloon when the anvil drops?
Fballoon
mg
http://www.lghs.net/ourpages/users/dburns/RRPhysics/R
The Cartoon Laws of Physics:
•Any body suspended in space will
remain in space until made aware of its
situation.
•Everything falls faster than an anvil.
•All principles of gravity are negated by
fear.
Iclicker #3
A person pulls a block of mass
M across a frictionless floor
with a force F as shown in the
figure. Which of the following
statements is true?
F
M
A. The normal force of the table on the block is equal to the
weight of the block
B. The block will accelerate to the right with an acceleration
given F/M
C. The block moves at constant velocity
D. The force of the block on the table is less then the weight
of the block
E. If the force is large enough, the block will lift off the floor
Iclicker Question #3
In which direction will mass m2 move?
A)
B)
C)
D)
E)
Up the incline
Down the incline
It will not move at all
It depends on the exact value of gravitational acceleration g.
We don’t know. It depends on values for m1, m2, and .
Iclicker Question #4
Under what condition will mass m2 move UP the incline.
A)
B)
C)
D)
E)
m1  m2
m1  m2
m1  m2 sin 
m1  m2 sin 
m1  m2 sin 
```