Transcript DynQuestions - University of Manchester

Chris Parkes
Dynamics Questions
Motion
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?
s
s
00
00
t
s
s
t 00
t 00
s
t
00
t
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?
v
v
00
00
t
v
v
t 00
t 00
v
t
00
t
Projectiles
• Cannons firing shells of varying masses at
different angles and velocities.
• Which has the greatest range ?
v
(neglecting air resistance) y

x,y,t
x
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)
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 driver’s average speed for the
trip?
1)
2)
3)
4)
5)
0.85v
0.80v
0.75v
0.70v
0.65v
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 ?
1. Dropped bullet
2. Fired bullet
3. Both at same time
Newton’s Laws
Newton 2
1)
2)
1kg
2kg
4)
3)
3kg
4kg
3kg
5kg
6kg
10kg
• In which diagram will the magnitude of the
acceleration be the largest?
The Levi logo has
Horse
Horse
• What happens if I replace one of the horses
with a fence post – does this ?
Horse
Post
1. Cut tension on jeans by one half
2. Not change tension
3. Double tension
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 > w
3. n < w
4. not enough information given to decide
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 > w2
3. T < w2
4. not enough information given to decide
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
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 6.00–kg 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
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 actionreaction pair. What force is the other
half?
1. the force of the Earth’s 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
Work & Energy
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
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
1) 0m/s
4) 30m/s
2) 10m/s
5) 40m/s
3) 20m/s
6) won’t make it
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
1) 0m/s
4) 30m/s
2) 10m/s
5) 40m/s
3) 20m/s
6) won’t make it
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
1) 0m/s
4) 30m/s
2) 10m/s
5) 40m/s
3) 20m/s
6) won’t make it
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?
1. Rubber bullet
2. Aluminium bullet
3. Both same
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
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
Blocks-1
F
2m
• Three blocks are pushed by equal forces F over a
frictionless surface for 2m.
• Mass of block A > mass B > 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
Blocks-2
F
2m
• Three blocks are pushed by equal forces F over a
frictionless surface for 2m.
• Mass of block A > mass B > 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
Blocks 3
F
2m
• Three blocks are pushed by equal forces F over a
frictionless surface for 2m.
• Mass of block A > mass B > 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
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
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 ?
1)
mv 2
k
2)
mv
k
3)
mv 2
2k
4) mv k
SHM
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
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
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
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
side…how long does the swing
take?
1.
2.
3.
4.
0.5 s
1s
2s
3s

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
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 object’s maximum speed
both double
2. the oscillation period remains the same and the
object’s maximum speed doubles
3. the oscillation period and the object’s maximum speed
both remain the same
4. the oscillation period doubles and the object’s
maximum speed remains the same
5. the oscillation period remains the same and the
object’s maximum speed increases by a factor of 21/2
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
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
Circular Motion
Angular Momentum
Pull a pendulum to one side let it
go. As it swings back and
forwards…..
1. Both angular and linear momentum are
conserved
2. Only angular momentum
3. Only linear momentum
4. neither
Q9.3
A DVD is rotating with an everincreasing speed.
Compared to the point P on the
disc’s surface, the point Q on the
disc’s 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
Q9.4
Angular Velocity
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
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
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
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 Earth’s 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
Q12.4
A satellite is moving around the
Earth in a circular orbit. Over the
course of an orbit, the Earth’s
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
Q12.6
A planet (P) is moving
around the Sun (S) in an
elliptical orbit. As the
planet moves around the
orbit, the planet’s 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
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
Q9.5
Moment of Inertia
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