Transcript Force and Motion

Review
Two balls are thrown from the top of a cliff.
Ball S is thrown upwards at the same time
Ball T is thrown out horizontally.
A. Ball T will hit the ground first.
B. Ball S will hit the ground first.
C. Ball S and Ball T will hit the ground at the
same time.
D. We must know the masses of Ball S and
Ball T to answer this question.
Review
A cannon fires a shell at a target 1200 meters away on a
horizontal flat plane. Ignoring air resistance, while the shell is
in flight, which statement correctly describes the acceleration
the shell experiences?
A. The acceleration changes with time and acts only
horizontally.
B. The acceleration is the same at every point along the
pathway and acts only vertical.
C. The shell experiences no acceleration.
D. The shell experiences an acceleration in both the
horizontal and vertical direction.
E. The shell experiences an acceleration that changes with
time and acts only in the vertical direction.
Review
Ball S is projected horizontally at the same
time Ball T is released and allowed to fall.
The motion of both balls begins from the
same height.
A. Ball T will reach the ground first.
B. Ball S will reach the ground first.
C. Balls S and T will reach the ground at the
same time.
D. We must know the masses to decide.
A projectile is shot with a speed of 25 m/s straight off a
building that is 41 m high. What is the range (dx)?
d = .5 at 2
t = √d/.5a
t = √41/(.5 x 9.8 m/s2)
t = 2.89s
d x= vit
dx = (25 m/s )(2.89s)
dx = 72.25 m
Review
Which of the following is NOT a vector
quantity?
A. force
B. speed
C. velocity
D. acceleration
How do you determine force of
weight
• Multiply mass times 9.8!
How do you determine normal
force
• It equals weight in most cases!
What does net force mean?
• Margin of victory for the winning side!
FNET = 60 N down
What is A & B?
A = 12 N
B = 75 N
35 N
A
12 N
20 N
B
What is the missing force?
20 N
?N
10 kg
15 N
-5 m/s2
Fnet is 50 N left, so force to the left is 85 N
Review
All forces occur in pairs
A. true
B. false
Review
An object requires a net force to be in motion
A. true
B. false
Review
What a good example of the 1st law?
Remember 1st law is aka Law of Inertia
Review
What a good example of the 2nd law?
Review
What a good example of the 3rd law?
Remember 3rd law implies 2 forces and 2
objects!
1.
2.
3.
4.
CAN YOU SOLVE PROBLEMS LIKE THIS?
What is the weight of a 15 kg rock?
147 N
A skateboard (mass 12 kg ) accelerates from rest to 3.8 m/s over a
distance of 9.4m. What is the skateboard ’s rate of acceleration?
0.768 m/s2
What force was applied to the skateboard in to achieve this rate of
acceleration?
9.22 N
An unbalanced force of 25 N is applied to a 12.5-kg mass. What
should be the acceleration experienced by the mass?
2 m/s2