Dynamics Questions

1
Dynamics Questions
Chris Parkes

2
Motion
3
s-t graph

• I drop a ball out of the window of my office (4th
  floor) which graph best represents the distance
  travelled by the ball before it hits the ground?

4
v-t graph

• I drop a ball out of the window of my office (4th
  floor) which graph best represents the velocity
  of the ball before it hits the ground?

5
Projectiles

• Cannons firing shells of varying masses at
  different angles and velocities.
• Which has the greatest range ?
• (neglecting air resistance)

1) m 1Kg ? 30º V 57.7 m/s (Vx 50 m/s Vy
28.9 m/s)
2) m 1Kg ? 45º V 70.7 m/s (Vx 50 m/s Vy
50 m/s)
3) m 2Kg ? 45º V 70.7 m/s (Vx 50 m/s Vy
50 m/s)
4) m 2Kg ? 60º V 100 m/s (Vx 50 m/s Vy
86.6 m/s)
6
speed

• A driver travels ¾ of his trip distance at one
  velocity (v) gets caught by a speed camera and
  completes it at half this velocity (½ v).
• What was the drivers average speed for the trip?

• 0.85v
• 0.80v
• 0.75v
• 0.70v
• 0.65v

7
Dropped bullet

• One bullet is fired from a gun.
• At the same time another is simply dropped from
  the same height.
• Which hits the ground first ?

• Dropped bullet
• Fired bullet
• Both at same time

8
Newtons Laws
9
Newton 2
4)
1)
2)
3)

• In which diagram will the magnitude of the
  acceleration be the largest?

10
The Levi logo has
Horse
Horse

• What happens if I replace one of the horses with
  a fence post does this ?

Horse
Post

• Cut tension on jeans by one half
• Not change tension
• Double tension

11
Q5.2
A cable attached to the car holds the car at rest
on the frictionless ramp (angle a).
The ramp exerts a normal force on the car. How
does the magnitude n of the normal force compare
to the weight w of the car?
1. n w 2. n gt w 3. n lt w 4. not enough
information given to decide
12
Q5.4
A cart (mass m1, weight w1) is attached by a
lightweight cable to a bucket (mass m2, weight
w2) as shown.
The ramp is frictionless. The pulley is
frictionless and does not rotate. When released,
the cart accelerates up the ramp and the bucket
accelerates downward.
Which statement about the cable tension
(magnitude T) is correct?
1. T w2 2. T gt w2 3. T lt w2 4. not enough
information given to decide
13
Q4.1
You are standing at rest and begin to walk
forward. What force pushes you forward?
1. the force of your feet on the ground 2. the
force of your acceleration 3. the force of your
velocity 4. the force of your momentum 5. the
force of the ground on your feet
14
Q4.4
A woman pulls on a 6.00-kg crate, which in turn
is connected to a 4.00-kg crate by a light rope.
The light rope remains taut. Compared to the
6.00kg crate, the lighter 4.00-kg crate
1. is subjected to the same net force and has the
same acceleration 2. is subjected to a smaller
net force and has the same acceleration 3. is
subjected to the same net force and has a smaller
acceleration 4. is subjected to a smaller net
force and has a smaller acceleration 5. none of
the above
15
Q4.2
An apple sits at rest on a horizontal table
top. The gravitational force on the apple (its
weight) is one half of an action-reaction pair.
What force is the other half?
1. the force of the Earths gravity on the
apple 2. the upward force that the table top
exerts on the apple 3. the upward force that the
apple exerts on the Earth 4. the downward force
that the apple exerts on the table top 5. the
frictional force between the apple and the table
top
16
Work Energy
17
Q6.3
Two iceboats (one of mass m, one of mass 2m) hold
a race on a frictionless, horizontal, frozen
lake. Both iceboats start at rest, and the wind
exerts the same constant force on both iceboats.
Which iceboat crosses the finish line with more
kinetic energy (KE)?
1. the iceboat of mass m it has twice as much KE
as the other 2. the iceboat of mass m it has 4
times as much KE as the other 3. the iceboat of
mass 2m it has twice as much KE as the other 4.
the iceboat of mass 2m it has 4 times as much KE
as the other 5. they both cross the finish line
with the same kinetic energy
18
Roller Coaster -1

• A car moves along the track as shown.
• At a the car is moving with 10 m/s.
• Neglecting friction, how fast will the car be
  moving at B ?

10m/s
A
B
60m
60m
10m

• 0m/s 2) 10m/s 3) 20m/s
• 4) 30m/s 5) 40m/s 6) wont make it

19
Roller Coaster -2

• A car moves along the track as shown.
• At A the car is moving with 10 m/s.
• Neglecting friction, how fast approx. will the
  car be moving at B ?

10m/s
A
60m
B
20m
10m

• 0m/s 2) 10m/s 3) 20m/s
• 4) 30m/s 5) 40m/s 6) wont make it

20
Roller Coaster -3

• A car moves along the track as shown.
• At a the car is moving with 10 m/s.
• Neglecting friction, how fast will the car be
  moving at B ?

10m/s
A
B
60m
65m
10m

• 0m/s 2) 10m/s 3) 20m/s
• 4) 30m/s 5) 40m/s 6) wont make it

21
Bullets

• A rubber bullet and an aluminium bullet have same
  size,speed, mass. They are fired at a block of
  wood. Which is most likely to knock the block
  over?

• Rubber bullet
• Aluminium bullet
• Both same

22
Q8.1
A ball (mass 1.0 kg) is initially moving to the
left at 30 m/s. After hitting the wall, the ball
is moving to the right at 20 m/s. What is the
impulse of the net force on the ball during its
collision with the wall?
1. 50 kg m/s to the right 2. 50 kg m/s to the
left 3. 10 kg m/s to the right 4. 10 kg m/s
to the left 5. none of the above
23
Q8.4
Two objects with different masses collide and
stick to each other. Compared to before the
collision, the system of two gliders after the
collision has
1. the same total momentum and the same total
kinetic energy 2. the same total momentum but
less total kinetic energy 3. less total momentum
but the same total kinetic energy 4. less total
momentum and less total kinetic energy 5. not
enough information given to decide
24
Blocks-1
2m
F

• Three blocks are pushed by equal forces F over a
  frictionless surface for 2m.
• Mass of block A gt mass B gt mass C
• Which will have the largest kinetic energy?
• 1) block A
• 2) block B
• 3) block C
• 4) all have same K.E.
• 5) depends on precise masses

25
Blocks-2
2m
F

• Three blocks are pushed by equal forces F over a
  frictionless surface for 2m.
• Mass of block A gt mass B gt mass C
• Which will be travelling fastest?
• 1) block A
• 2) block B
• 3) block C
• 4) all have same speed
• 5) depends on precise masses

26
Blocks 3
2m
F

• Three blocks are pushed by equal forces F over a
  frictionless surface for 2m.
• Mass of block A gt mass B gt mass C
• Which will have received the greatest impulse
  during the 2m push?
• 1) block A
• 2) block B
• 3) block C
• 4) all will have same impulse
• 5) depends on precise masses

27
Q6.4
A tractor driving at constant speed pulls a sled
loaded with firewood. There is friction between
the sled and the road.
After the sled has moved a distance d, the total
work done on the sled is
1. positive 2. negative 3. zero 4. not enough
information given to decide
28
Spring

• A lab cart mass m velocity v crashes into a
  spring and compresses the spring with spring
  constant k.
• What is the maximum compression of the spring ?

29
SHM
30
Q13.2
This is an x-t graph for an object in simple
harmonic motion.
At which of the following times does the object
have the most negative acceleration ax?
1. t T/4 2. t T/2 3. t 3T/4 4. t T
31
Q13.3
To the right is an x-t graph for an object in
simple harmonic motion. Which of the graphs below
correctly shows the velocity versus time for
this object?
1. graph I 2. graph II 3. graph III 4. graph IV
32
Q13.4
To the right is an x-t graph for an object in
simple harmonic motion. Which of the graphs below
correctly shows the acceleration versus time for
this object?
1. graph I 2. graph II 3. graph III 4. graph IV
33
Pull a pendulum one degree to one side let it go.
It takes 1s to swing to vertical.Now pull it two
degrees to the sidehow long does the swing take?

• 0.5 s
• 1s
• 2s
• 3s

?
34
Q13.7
A simple pendulum consists of a point mass
suspended by a massless, unstretchable string. If
the mass is doubled while the length of the
string remains the same, the period of the
pendulum
1. becomes 4 times greater 2. becomes twice as
great 3. becomes 21/2 times greater 4. remains
unchanged 5. decreases
35
Q13.1
An object on the end of a spring is oscillating
in simple harmonic motion. If the amplitude of
oscillation is doubled,
1. the oscillation period and the objects
maximum speed both double 2. the oscillation
period remains the same and the objects maximum
speed doubles 3. the oscillation period and the
objects maximum speed both remain the same 4.
the oscillation period doubles and the objects
maximum speed remains the same 5. the
oscillation period remains the same and the
objects maximum speed increases by a factor of
21/2
36
Q13.5
This is an x-t graph for an object connected to a
spring and moving in simple harmonic motion.
At which of the following times is the potential
energy of the spring the greatest?
1. t T/8 2. t T/4 3. t 3T/8 4. t T/2 5.
More than one of the above
37
Q13.6
This is an x-t graph for an object connected to a
spring and moving in simple harmonic motion.
At which of the following times is the kinetic
energy of the object the greatest?
1. t T/8 2. t T/4 3. t 3T/8 4. t T/2 5.
More than one of the above
38
Circular MotionAngular Momentum
39
Pull a pendulum to one side let it go. As it
swings back and forwards..

• Both angular and linear momentum are conserved
• Only angular momentum
• Only linear momentum
• neither

40
Q9.3
A DVD is rotating with an ever-increasing speed.
Compared to the point P on the discs surface,
the point Q on the discs surface has
1. the same centripetal acceleration and the same
tangential acceleration 2. a greater centripetal
acceleration and a greater tangential
acceleration 3. a smaller centripetal
acceleration and a smaller tangential
acceleration 4. a greater centripetal
acceleration and the same tangential
acceleration 5. none of the above
41
Angular Velocity
Q9.4
Compared to a gear tooth on the rear sprocket (on
the left, of small radius) of a bicycle, a gear
tooth on the front sprocket (on the right, of
large radius) has
1. a faster linear speed and a faster angular
speed 2. the same linear speed and a faster
angular speed 3. a slower linear speed and the
same angular speed 4. the same linear speed and a
slower angular speed 5. none of the above
42
Q12.1
The mass of the Moon is 1/81 of the mass of the
Earth. Compared to the gravitational force that
the Earth exerts on the Moon, the gravitational
force that the Moon exerts on the Earth is
1. 812 6561 times greater 2. 81 times greater
3. equally strong 4. 1/81 as great 5. (1/81)2
1/6561 as great
43
Gravity

• The gravitational force on a copy of University
  Physics at the top of Ben Nevis is 40N.
• What would the approximate gravitational force be
  on the same book on a mountain twice as high ?
• 1) 5N
• 2) 10 N
• 3) 20 N
• 4) 40 N
• 5) 80N

44
Q12.2
The planet Saturn has 100 times the mass of the
Earth and is 10 times more distant from the Sun
than the Earth is. Compared to the Earths
acceleration as it orbits the Sun, the
acceleration of Saturn as it orbits the Sun is
1. 100 times greater 2. 10 times greater 3. the
same 4. 1/10 as great 5. 1/100 as great
45
Q12.4
A satellite is moving around the Earth in a
circular orbit. Over the course of an orbit, the
Earths gravitational force
1. does positive work on the satellite 2. does
negative work on the satellite 3. does positive
work on the satellite during part of the orbit
and negative work on the satellite during the
other part 4. does zero work on the satellite at
all points in the orbit
46
Q12.6
A planet (P) is moving around the Sun (S) in an
elliptical orbit. As the planet moves around the
orbit, the planets angular momentum
1. increases as it moves from aphelion to
perihelion and decreases as it moves from
perihelion to aphelion 2. decreases as it moves
from aphelion to perihelion and increases as it
moves from perihelion to aphelion 3. increases at
all times 4. decreases at all times 5. remains
the same at all times
47
Q8.6
A yellow object and a red object are joined
together. Each object is of uniform density.
The center of mass of the combined object is at
the position shown by the green X.Which object
has the greater mass, the yellow object or the
red object?
1. the yellow object 2. the red object 3. they
both have the same mass 4. not enough information
given to decide
48
Moment of Inertia
Q9.5
All three of these objects are uniform, have the
same mass, and have the same outer dimension.
Which has the smallest moment of inertia about an
axis through its center as shown?
1. the solid cylinder 2. the hollow cylinder 3.
the rectangular solid 4. not enough information
given to decide