Review Questions Chapter 3
Pages 40-41 #1-18
1. How does a vector quantity differ from a
scalar quantity? (3.1)
• A vector quantity includes an objects direction
of motion or force.
• A vector quantity has both magnitude and
direction.
• A scalar quantity only includes magnitude.
2. Why is speed classified as a scalar quantity
and velocity classified as a vector quantity?
(3.1)
• Speed has no particular direction, velocity
specifies direction.
• Speed = scalar
• Velocity = vector
3. If a vector that is 1 cm long represents a velocity
of 10 km/h, what velocity does a vector 2 cm long
drawn to the same scale represent?(3.2)
•
•
•
•
If 1 cm = 10 km/h
Then 2 cm = 20 km/h
3 cm = 30 km/h
What velocity would 0.5 cm equal? 1.5 cm?
• ANSWER: 5 km/h and 15 km/h
4. When a rectangle is constructed in order to add
velocities, what represents the resultant of velocities?
(3.2)
• The diagonal represents the resultant
velocities.
5. Why do we say a rectangle is a special case of
a parallelogram? (3.2)
• A rectangle is a special case of parallelogram
because if has four sides, with two pairs of
sides parallel to each other.
• Also a rectangle has right angles.
6. Will a vector at 45o to the horizontal be larger or
smaller than its horizontal and vertical components?
By how much? (3.3)
• The vector will be larger.
• The vector will be the square root of 2 or
1.414 times greater than either of its
components.
7. Why does a bowling ball move without
acceleration when it rolls along a bowling alley? (3.4)
• There is no acceleration because there is no
horizontal component of force.
• The only force acting on the bowling ball once
it is released from the bowler’s hand, is the
vertical force of gravitational acceleration.
8. In the absence of air resistance, why does the horizontal
component of velocity for a projectile remain constant while
the vertical component changes? (3.4)
• The only force acting on a projectile is
gravitational acceleration. “g” does not have a
horizontal component, therefore there is no
change to the horizontal velocity.
9. How does the downward component of the
motion of a projectile compare with the motion of
free fall? (3.4)
• The downward component of a projectile’s
motion and the motion of free fall are the
same.
• Both are under the influence of gravity.
10. At the instant a ball is thrown horizontally over a level range, a ball
held at the side of the first is released and drops to the ground. If air
resistance is neglected, which ball strikes the ground first? (3.4)
• They hit the ground at the same time. The
only force acting on each ball is the vertical
gravitational component.
11a. How far below an initial straight-line path will a projectile fall in
one second? (3.5)
b. Does your answer depend on the angle of launch or the initial
speed of the projectile? (3.5)
• In one second a projectile will fall 5m.
• Neither, because the only force acting on a
projectile is the gravity. Gravitational force
only exerts in the vertical downward direction.
Therefore, the vertical displacement (distance)
is found using the formula for free fall.
• d=1/2 gt2
12. At what angle should a slingshot be oriented for
maximum altitude? For maximum horizontal range?
(3.5)
• For maximum altitude a slingshot should be
orientated straight up.
• For maximum horizontal range, a slingshot
should be oriented at a 45 degree angle.
13. Neglecting air resistance, if you throw a ball straight up
with a speed of 20 m/s, how fast will it be moving when you
catch it? (3.5)
• It will be moving at 20 m/s when you catch it.
14. Neglecting air resistance, if you throw a baseball at 20 m/s to your friend at first
base, will the catching speed be greater than, equal to, or less than 20 m/s?
Does the speed change if air resistance is a factor? (3.5)
• The catching speed will be equal to the
throwing speed, 20 m/s.
• If air resistance is a factor, the speed will
change. Air resistance will slow down the
catching speed of the ball.
15. What do we call a projectile that continually “falls”
around the Earth? (3.6)
• We call this type of projectile an Earth
satellite.
16. How fast must a projectile moving horizontally
travel so that the curve it follows matches the curve
of the Earth? (3.6)
• It must travel approximately 8 km/s (18 000
mi/h) if the satellite is close to the Earth.
17. Why is it important that such a satellite be
above Earth’s atmosphere? (3.6)
• It is important so the satellite avoids the
heating effects of atmospheric friction.
18. What force acts on a satellite that is above
the Earth’s atmosphere? (3.6)
• The only force that acts on a satellite that is
above the Earth’s atmosphere is gravity.
• This is truly a “friction free physics world”
because there is no air resistance beyond the
Earth’s atmosphere.