#### Transcript mDv

The graph represents relative position down your sidewalk, as you walk
b
a
c
d
Time (s)
When are you moving fastest?
I drive 3 miles west, down 25 mile road, then turn around and drive 4 miles
east.
Describe my displacement and distance traveled
I am jogging eastward down the sidewalk at 2 m/s, and slow to a stop over
4 seconds.
- 0.5 m/s2
What is my acceleration?
Based on the graph of a car’s velocity over time, in what region is the
magnitude of the car’s acceleration greatest?
velocity (m/s)
b
c
a
d
time (s)
The Moon is in an almost circular orbit around the Earth. Describe it’s
acceleration.
A car’s motion is described in the velocity v. time graph
7
Velocity (m/s)
6
5
b
4
3
c
a
2
1
1
2
3
4
5
6
time (s)
Describe the cars motion
Calculate the car’s acceleration in each segment
Calculate the total distance the car traveled
7
A pendulum is swinging back and forth. If motion to the right is
considered positive, when is the velocity of the pendulum negative?
When is the acceleration negative?
I shoot a rocket with an initial speed of 100 m/s at an angle of 45°
above the horizontal. What is the vertical component of the rocket’s
initial velocity?
What if the angle was 30°?
Which is the magnitude of the gravitational force acting on me?
a. my weight
b. my mass
c. zero, because I am not moving
d. 9.81 N
What is the net force acting on the box?
15 N
20 N
I hit a nail with a hammer with 100 Newtons of downward force.
What other force is involved? (think of Newton’s 3rd Law)
Why does the nail in the previous question move downward?
Playing “tug of war”, the juniors pull left with a force of 1000 N,
the seniors pull right with a force of 1250 N. What is the effect of these
forces on movement?
A 10 kg box is pushed left with a force of 20 N against a 10 N
frictional force. What is the acceleration of the box?
What force keeps a car from slipping off a circular race track?
I kick my 0.25 kg calculator horizontally off of Ike’s 8 m tall
roof, with an initial velocity of 2 m/s. What is the initial acceleration
of the calculator?
How does changing time of impact change the force?
FDt = mDv
What happens to gravitational force if the distance is cut in half?
ex. A 20 N gravitational force exists between two objects 100 m apart.
What would the force be if they were 50 m apart? What if the mass is
tripled?
What happens to gravitational force if the mass of one object
is doubled? Be able to calculate gravitational force, given mass and distance
Draw vectors for force and velocity in the orbital drawing
v
F
In an inelastic collision (things stick together),
m1v1 + m2v2 = (m1 + m2)vf
If I throw a 2 kg clay ball forward at 10 m/s, and my friend throws
a 1 kg clay ball forward at 20 m/s, what will their speed be when they
hit and stick together?
For work to occur, only the force that is parallel to the motion applies.
I place a 5 kg mass on a tabletop, from the floor, 1.3 m high. How
much work did I do?
What type of energy is found in a mass held up in the air? In a falling
mass? In a stretched out slinky?
I throw a 2 kg ball from my shoulder height of 1.8 m to 5 m.
What its gain in potential energy?
What will be the speed of the previous ball, when it hits the ground?
Why does a car skid when going too fast around a curve?
I am pushing a box across the floor. How does the magnitude
of the force I am pushing on the box compare to the magnitude of
the force that the box is pushing on me?
I am lifting a 20 kg mass by a rope with constant speed.
What is the tension in the rope?
F = ma
A 2 kg wood block slows from 10 m/s to rest, while sliding across
the floor in 5 seconds. What is the force of friction that stopped it?
If an object is moving at constant velocity, what can you say
about the net force acting on the object?
A car has a net force of 50000 N and accelerates at 20 m/s2.
What is the mass of the car?
Know the difference between speed and velocity.
position (m)
3
2
1
0
-1
-2
-3
2
4
6
8
10
12
14
16
time (s)
What is the average velocity between 0 and 10 seconds?
What is the velocity between 7 seconds and 10 seconds?
What distance is from 0 to 6 seconds?
Describe force, acceleration, velocity and
displacement at position A, B and C
A
equilibrium
B
C
Which two forces will produce the greatest acceleration?
a
b
c
d
e
Which is the correct velocity vector for a ball traveling counter clockwise
on the circle?
If the ball were released from the circle, which way would it go?
50
position (m)
40
What is the average velocity of the
graphed object?
30
20
10
2 4 6 8 10 12 14 16 18
time (s)
A ball is dropped and when it hits the ground is going 20 m/s.
How high was it dropped from?
How fast would the ball have to be thrown upward to reach that height?
A 20 kg clay ball traveling at 30 m/s right collides with a 10 kg clay
ball traveling at 40 m/s to the left. What is the final velocity of the
pair? Which had the greatest change in velocity?
20 kg
30 m/s
10 kg
40 m/s
m1v1 + m2v2 = (m1 + m2)vf
(20 kg)(30 m/s) + (10 kg)(-40 m/s) = (30 kg)vf
vf = 6.7 m/s
ball traveling left had the greatest change in velocity
The total momentum before impact equals the total momentum after!
I drop my calculator from a tall 100 m cliff. How long does it take
to hit the ground?
I run a lap on a 400 m track in 48 seconds. What is my average velocity?
Centripetal Force is the force that holds something in circular
motion, it accelerates towards the center of a circle.
a
b
c
d
e