Transcript Electric Potential - McMaster University

Final Exam
Wed April 18 – 2pm – check the schedule for rooms!
2 hours long – 30 MC questions
Covers all material with approximately equal weight, up
to and including the final lecture on fluids.
Review questions will be posted on the website later today !
Physics 1B03summer-Lecture 13
Office Hours
I’ll be in my office between 12-2pm on these
days (posted on the website):
•
•
•
•
Tuesday Apr 10
Wednesday Apr 11
Tuesday Apr 17
Wednesday Apr 18 (11am – 1pm)
Physics 1B03summer-Lecture 13
Uncertainty
Assume that a is related to measurable quantities , F, m and θ
by Fsinθ=ma. The absolute uncertainty in a is:
Physics 1B03summer-Lecture 13
Example 1
You are pushing a 50kg
block with a force of 100 N
over a surface with μs=0.15
and μk=0.1.
With what force does the
block push back on you ?
!@%&*#$

Fg

FA

f

n
Ans: 49N
Physics 1B03summer-Lecture 13
Example 2
You are pushing a 50kg
block with a force of 100 N
over a surface with μs=0.15
and μk=0.1.
What is the work done by
the force of friction if you
push the block for 5m ?
!@%&*#$

Fg

FA

f

n
Ans: -245J
Physics 1B03summer-Lecture 13
Example 3
A block of 3kg is pushed with a force FA=40N at an angle of
45 degrees to the horizontal. If μk = 0.1, find the acceleration.
FA
θ
m
Physics 1B03summer-Lecture 13
Projectile Motion
y=voyt-½gt2
- resolve motion into x/y
- x and y position equations
- x and y velocity components
x=voxt
y
vo
x
Physics 1B03summer-Lecture 13
Concept Quiz
A tennis ball is placed on top of a basketball and both are dropped.
The basketball hits the ground at speed v0. What is the maximum
speed at which the tennis ball can bounce upward from the
basketball? (For “maximum” speed, assume the basketball is
much more massive than the tennis ball, and both are elastic).
a) v0
b) 2v0
c) 3v0
?
v0
-elastic collision
-relative velocity
v0
Physics 1B03summer-Lecture 13
Example 3
• A 100 g baseball is thrown with a speed of 10m/s. It is hit
straight back toward the pitcher at a speed of 30m/s. The
interaction force is shown by the graph:
F
Fmax
6ms
t
What is the maximum force Fmax that the bat exerts on the
ball ?
Physics 1B03summer-Lecture 13
Example 5
A bullet of mass m moving with velocity v is shot into a block
of mass M that is at rest on the edge of a table. If the bullet
embeds in the block, determine the velocity of the system.
How far would the system fall if it was sitting at the edge of a
table of height h ? – use projectile motion !
Physics 1B03summer-Lecture 13
Gravitational Work
When the block is lowered,
gravity does work.
The work done is path
independent !!! So, in both
cases it is:
mg
y
s1
s2
W=mgs1=mgs2
Physics 1B03summer-Lecture 13
Example 7
A block of mass m = 2.0 kg starts to
slides at speed v0 = 3.0 m/s on a
table with μk=0.1. After 5m it hits a
spring with k = 400 N/m.
v0
If at the point the block hits the
spring the friction is gone, how far
will the spring compress before the
block stops?
Physics 1B03summer-Lecture 13
Constructive Interference:
Δr = m λ
dy
 m
L
2t  m
m = 0, ±1, ±2, …
<- for double slit
<- for thin film
Remember: low to high, phase shift of pi (=λ/2)
also, don’t forget ‘n’ -> λ/n
Physics 1B03summer-Lecture 13
Destructive Interference:
Δr = (m + ½)λ
dy
1
 ( m  )
L
2
1
2t  (m  )
2
m = 0, ±1, ±2, …
<- for double slit
<- for thin film
Remember: low to high, phase shift of pi (=λ/2)
also, don’t forget ‘n’ -> λ/n
Physics 1B03summer-Lecture 13
Example 8
What is the minimum thickness of a layer of gasoline
(n  1.3) floating on water (n=1.5) needed to produce
destructive interference for light with a 500nm
wavelength ? (air : n  1.00).
Physics 1B03summer-Lecture 13