Transcript HW 11 II - III - Fort Thomas Independent Schools

Page 81 (Ch. 5.4-5.5)
• 6. The bowling ball moves without acceleration because
there is no net force on the ball (neglecting friction)
• 7. Neglecting air resistance, the horizontal component
of velocity for a projectile remains constant due to its
inertia. The vertical component is accelerated due to
gravity.
• 8. The downward component of motion of projectile is
the same as free fall, since they are both under the
influence of gravity.
• 27. Not at all! Although both inertial horizontal motion
and vertical accelerated motion combine to form a
curved, parabolic path, neither depends on the other.
Additional Questions
B
1. A projectile is an object that moves
through the air under the influence of
gravity.
2. The curved path of a projectile is a result
of the combination of horizontal motion at
a constant velocity and vertical motion
that is accelerated at 9.8 m/s2
Additional Questions
II B
3. 5.8 a represents horizontal motion at a
constant velocity and 5.8 b demonstrates
vertical motion that is acceleration.
4. Same: both fall at the same rate. Different is
that the yellow ball is also moving horizontally
while the red ball falls straight down.
5. Parabola is the curved shape of a projectile’s
path, and trajectory is the path taken by the
projectile.
Additional Questions
• III. A) Pg. 99-100
• 13. Freefall occurs when an object is falling and
only experiences the force of gravity.
• 15. Greater mass means proportionally greater
weight, and proportionally more force. The force
(or weight) to mass ratio always produces the
same rate of acceleration. Since there is no air
resistance in freefall, the difference in weights
(or masses) does not change acceleration.
Additional Questions, pg. 100)
• 16. Air resistance acting on an object increases with
increasing speed.
• 17. The object at the greater speed encounters more air
resistance.
• 18. The acceleration equals zero at terminal velocity
because the weight of the falling object is balanced by
air resistance, so the net force equals zero.
• 19. Air resistance is also affected by surface area (the
greater the surface area, the greater the air resistance).
• 20. 100-N of weight is balanced by 100-N of air
resistance at terminal velocity.
Additional Questions
• III b)
• 1. Net force equals the weight of the object.
• 2. Air resistance is dependent upon the object’s
surface area and speed.
• 3. Air resistance can be reduced by improving
the aerodynamics (stream lining) or by lessening
the surface area. It would also be possible by
applying brakes to a car to reduce speed.
Additional Questions
• III b)
• 4. The elephant experiences the greater air
resistance, because the elephant has a greater
surface area, and would be falling faster than
the paper.
• Note: the rate of acceleration and the net force
acting on the two objects are directly related.
More net force means more acceleration, which
means that the object can increase in speed. It
does not take much air resistance to balance the
weight of the paper, but it will take a great deal
of air resistance to balance the weight of the
elephant (to reach equilibrium). Thus, the
elephant must be falling at large rate of speed to
reach terminal velocity.
Additional Questions
• III b)
• 5. Terminal speed (or velocity) is the maximum falling
speed an object can reach.
• 6. Air resistance and weight are balanced at terminal
velocity.
• 7. terminal velocity (35 N of Fg balanced by 35 N of
Fair); free fall (only 35 N of Fg)
• 8. A feather has very little weight and a surface area
that is much greater than its width. It does not take
much air resistance to balance the weight of the feather,
so it reached terminal velocity quickly at a low rate of
speed.
• 9. Zero acceleration means that the object is moving at
a constant velocity; zero velocity means the object is at
rest.