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General Physics I
Lecture 1
Today's Concepts:
a) Displacement, Velocity, Acceleration
b) 1-D Kinematics with constant acceleration
Mechanics Lecture 1, Slide 1
Prelecture Example
Mechanics Lecture 1, Slide 4
Prelecture Example
Mechanics Lecture 1, Slide 5
Displacement and Velocity in 1-D
Displacement
Time taken
Mechanics Lecture 1, Slide 6
Displacement and Velocity in 1-D
The v(t) vs. t plot is just the
slope of the x(t) vs. t plot
Definition:
Speed = |v(t)|
Mechanics Lecture 1, Slide 7
Prelecture Question 1
The graph represents the position as a function of time for an
object in one-dimensional motion. Identify which statement
below correctly identifies the times at which the velocity of the
object is greater than zero.
A) The velocity is greater than 0 at t = 0 s and t = 4 s.
B) The velocity is greater than 0 at t = 2 s.
C) The velocity is greater than 0 at t = 0 s and t = 1 s.
D) The velocity is greater than 0 at t = 3 s and t = 4 s.
E) The velocity is greater than 0 at t = 0, 1, 3, and 4 s.
Mechanics Lecture 1, Slide 8
Clicker Question 1
Are the plots shown at the left
correctly related
A) YES
B) NO
Mechanics Lecture 1, Slide 9
Clicker Question 2
The velocity vs. time plot of some
object is shown to the right.
Which diagram below could be the
Displacement vs. time plot for the
same object?
A
B
C
Mechanics Lecture 1, Slide 10
Acceleration
Mechanics Lecture 1, Slide 11
Prelecture Question 2
The graph represents the velocity as a function of time for an
object in one-dimensional motion. Identify which statement
below correctly describes the motion at t = 3 s.
A) The object is slowing down and the
acceleration is negative.
B) The object is speeding up and the
acceleration is negative.
C) The object is slowing down and the
acceleration is positive.
D) The object is speeding up and the
acceleration is positive.
Mechanics Lecture 1, Slide 12
Checkpoint 1
For the Displacement and Velocity curves shown on the
left, which is the correct plot of acceleration vs. time?
A
A
B
Mechanics Lecture 1, Slide 13
Constant Acceleration
constant
a(t) = a
Mechanics Lecture 1, Slide 15
Checkpoint 2
At t = 0 a ball, initially at rest, starts to roll down a ramp with
constant acceleration. Suppose it moves 1 foot between
t = 0 sec and t = 1 sec.
How far does it move between t = 1 sec and t = 2 sec?
A) 1 foot B) 2 feet C) 3 feet D) 4 feet E) 6 feet
Mechanics Lecture 1, Slide 16
Clicker Question 3
?
5ft
1ft
9ft
16ft
At t = 0 a ball, initially at rest, starts to roll down a ramp with
constant acceleration. Suppose it moves 1 foot between
t = 0 sec and t = 1 sec.
How far does it move between t = 2 sec and t = 3 sec?
A) 1 foot B) 5 feet C) 9 feet D) 16 feet
Mechanics Lecture 1, Slide 17
The following questions pertain to the situation described below.
Two cars start from rest at a red stop light. When the light turns green, both cars
accelerate forward. The blue car accelerates uniformly at a rate of 4.6 m/s2 for
3.6 seconds. It then continues at a constant speed for 7.4 seconds, before
applying the brakes such that the car’s speed decreases uniformly coming to
rest 195.87 meters from where it started. The yellow car accelerates uniformly
for the entire distance, finally catching the blue car just as the blue car comes to
a stop.
1.
2.
3.
4.
5.
6.
How fast is the blue car going 1.8 seconds after it starts?
How fast is the blue car going 7.7 seconds after it starts?
How far does the blue car travel before its brakes are applied to slow down?
What is the acceleration of the blue car once the brakes are applied?
What is the total time the blue car is moving?
What is the acceleration of the yellow car?
Mechanics Lecture 1, Slide 19