Dynamics Questions

Chris Parkes

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?

00

s

t 00

s

t 00

s

t 00

s

t 00

s

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?

00

v

t 00

v

t 00

v

t 00

v

t 00

v

t

Projectiles• Cannons firing shells of varying masses at

different angles and velocities.

• Which has the greatest range ?

(neglecting air resistance)

x

y

x,y,t

v

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)

1) m= 1Kg = 30º V= 57.7 m/s (Vx = 50 m/s Vy = 28.9 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) 0.85v2) 0.80v3) 0.75v4) 0.70v5) 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

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

1kg

2kg

3kg

4kg

3kg

5kg

6kg

10kg

1) 2) 3) 4)

The Levi logo has

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

Horse Horse

Horse

Post

1. Cut tension on jeans by one half2. Not change tension3. Double tension

A cable attached to the car holds the car at rest on the frictionless ramp (angle ).

1. n = w

2. n > w

3. n < w

4. not enough information given to decide

Q5.2

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?

A cart (mass m1, weight w1) is attached by a lightweight cable to a bucket (mass m2, weight w2) as shown.

Q5.4

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.

1. T = w2

2. T > w2

3. T < w2

4. not enough information given to decide

Which statement about the cable tension (magnitude T) is correct?

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

Q4.1

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

Q4.4

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 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

Q4.2

Work & Energy

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.

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

Q6.3

Which iceboat crosses the finish line with more kinetic energy (KE)?

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 ?

60m

10m

10m/sA B

60m

1) 0m/s 2) 10m/s 3) 20m/s4) 30m/s 5) 40m/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 ?

60m

10m

10m/sA

B

20m

1) 0m/s 2) 10m/s 3) 20m/s4) 30m/s 5) 40m/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 ?

60m

10m

10m/sA B

65m

1) 0m/s 2) 10m/s 3) 20m/s4) 30m/s 5) 40m/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

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

Q8.1

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

Q8.4

Before collision

After collision

Blocks-1

• 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

F 2m

Blocks-2

• 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

F 2m

Blocks 3

• 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

F 2m

A tractor driving at constant speed pulls a sled loaded with firewood. There is friction between the sled and the road.

1. positive

2. negative

3. zero

4. not enough information given to decide

Q6.4

After the sled has moved a distance d, the total work done on the sled is

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 ?

kmv

kmv

kmv

kmv

)4

)3

)2

)1

2

2

2

SHM

This is an x-t graph for an object in simple harmonic motion.

1. t = T/4

2. t = T/2

3. t = 3T/4

4. t = T

Q13.2

At which of the following times does the object have the most negative acceleration ax?

1. graph I

2. graph II

3. graph III

4. graph IV

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?

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

Q13.4

1. 0.5 s

2. 1s

3. 2s

4. 3s

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?

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

Q13.7

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

Q13.1

This is an x-t graph for an object connected to a spring and moving in simple harmonic motion.

1. t = T/8

2. t = T/4

3. t = 3T/8

4. t = T/2

5. More than one of the above

Q13.5

At which of the following times is the potential energy of the spring the greatest?

This is an x-t graph for an object connected to a spring and moving in simple harmonic motion.

Q13.6

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 MotionAngular 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

A DVD is rotating with an ever-increasing 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

Q9.3

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

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

Angular Velocity

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

Q12.1

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

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

Q12.2

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

Q12.4

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

Q12.6

A yellow object and a red object are joined together. Each object is of uniform density.

1. the yellow object

2. the red object

3. they both have the same mass

4. not enough information given to decide

Q8.6

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?

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

Q9.5 Moment of Inertia