Transcript Forces Concept Review

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
An arrow is shot horizontally off a cliff. Which statement
correctly describes the acceleration of the arrow?
A. The acceleration changes with time and acts only
vertically.
B. The acceleration changes with time and acts only
horizontally.
C. The acceleration never changes and acts only vertically.
D. The arrow experiences no acceleration.
E. The arrow accelerates horizontally and vertically.
Review
An arrow is shot horizontally off a cliff. Which statement
correctly describes the velocity of the arrow?
A. The velocity changes and occurs only vertically.
B. The velocity changes and occurs only horizontally.
C. The velocity is constant horizontally and changes
vertically.
D. The velocity is constant and occurs only vertically.
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