Exam 2

Question 1

What is dynamics?

Answer 1

the relationship motion to the forces that cause it

Question 2

What is Newtons first law?

Answer 2

A body acted on by no net force moves with constant velocity (which may be zero) and zero acceleration.

Question 3

Frames of reference in which Newton’s 1st Law

is valid is called ______

Answer 3

inertial frame

Question 4

What is Newton’s 1st law often called?

Answer 4

Law of Inertia

Question 5

What is Newton’s Second Law?

Answer 5

If a net external force acts on a body, the body accelerates. The direction of acceleration is the same as the direction of the net force. The mass of the body times the acceleration of the body equals the net force vector.

Question 6

What is the unit for force?

Answer 6

kgm/s^2

Question 7

______ is directly proportional to the applied force.

Answer 7

Acceleration

Question 8

Acceleration is ______ proportional to the mass.

Answer 8

inversely

Question 9

What does mass characterize?

Answer 9

the inertial properties of a body. Weight is a force exerted on a body by the pull of the earth.

Question 10

______ acts all the time, even when the vector sum

is zero, even in free fall

Answer 10

Weight

Question 11

What is Newton’s third law?

Answer 11

If a body A exerts a force on body B (an “action”), then body B exerts a force on body A (a “reaction”). These two forces have the same magnitude but are opposite in direction. The two forces act on different bodies.

Question 12

_____ can keep an object from moving or slow its motion from what we last calculated on an ideal, frictionless surface.

Answer 12

Friction

Question 13

When a net force does work on a ____ body, it causes the body’s ______ to change.

Answer 13

rigid

speed

Question 14

When do you use the parallel component?

Answer 14

when the force acts at an angle

Question 15

Given Newton’s First Law of Motion, what do we reasonably expect an object to do when an object sits at rest with no unbalanced forces acting on it?

Answer 15

the object will remain at rest

Question 16

Given Newton’s First Law of Motion, what do we reasonably expect an object to do when an object is traveling with a constant velocity with no unbalanced forces acting on it?

Answer 16

the object will remain at the same speed, traveling in the same direction

Question 17

Given Newton’s First Law of Motion, what do we reasonably expect an object to do when an object sits at rest with an unbalanced force acting on it?

Answer 17

the object will begin to move with an increasing velocity

Question 18

A box rests on a horizontal surface. You apply a force on the box of F = 100 N at an angle, θ, below the horizontal and it slides at a constant velocity. The friction force that acts on the box is____

Answer 18

less than 100 Newtons

Question 19

A car is being lifted by a crane so that it moves upwards at a constant speed. Which force is doing negative work on the car as it is being lifted?

Answer 19

The force of gravity on the car due to the Earth

Question 20

A car is being lifted by a crane so that it moves upwards at a constant speed. Which force is doing positive work on the car as it is being lifted?

Answer 20

The force of the rope acting on the car

Question 21

A 500 lb steel beam is lifted up by a crane to a height of 100 ft and is held there. How much work is being done to hold the beam in place?

Answer 21

No work is being done to hold the beam in place

Question 22

Two blocks of unequal mass are tied together with a massless string that does not stretch and connected via a frictionless and massless pulley. Mass one, M1, rests on a frictionless table top. Mass two, M2, is released and both blocks begin to move. The blocks accelerate at the same rate since they are connected. What is the acceleration?

Answer 22

A value between zero and g

Question 23

A car traveling at 100km/hr strikes a bug and splatters it. The force of impact is____

Answer 23

the same for both

Question 24

A stalled car is being pushed up a hill at constant velocity by three people. The net force on the car is____

Answer 24

zero

Question 25

A sheet of paper can be withdrawn from under a container of milk without topplinging it if the paper is jerked because

Answer 25

the milk carton has inertia

Question 26

If a force always acts perpendicular to an object's direction of motion, that force cannot change the object's kinetic energy.

Answer 26

true

Question 27

If you find that twice as much work is needed to perform a task but it takes twice as much time, the amount of power required is

Answer 27

unchanged

Question 28

When a parachutist jumps from an airplane, he eventually reaches a constant speed, called the terminal speed. Once he has reached terminal speed______

Answer 28

the force of air drag on him is equal to his weight

Question 29

A ball drops some distance and gains 30J of kinetic energy. Do NOT ignore air resistance. How much gravitational potential energy did the ball loose?

Answer 29

more than 30J

Question 30

Neglecting friction, a small and a large block of ice begin sliding down an incline side-by-side (but not connected). The larger block reaches the bottom

Answer 30

at the same time as the small block

Question 31

A flower pot of mass m falls from rest to the ground below, a distance h. What is true about the KE of the pot

Answer 31

The KE of the pot when it hits the ground is proportional to h

Question 32

Two identical arrows, one with twice the speed of the other, are fired into a hay bale. The faster arrow will penetrate

Answer 32

four times further than the slower arrow

Question 33

Compared to a 1-kg block of solid iron, a 2-kg block of solid iron has twice as much

Answer 33

inertia mass volume

Question 34

Your weight is

Answer 34

the gravitational attraction force between you and the Earth

Question 35

An object's weight may properly be expressed in units of

Answer 35

newtons

Question 36

A force is a vector quantity because it has both

Answer 36

magnitude and direction

Question 37

An object is propelled along a straight-line path by a force. If the net force were doubled, the object's acceleration would be

Answer 37

twice as much

Question 38

An object is propelled along a straight-line path in space by a force. If the mass of the object somehow becomes twice as much, its acceleration

Answer 38

halves

Question 39

The force of friction on a sliding object is 10 newtons. The applied force needed to maintain a constant velocity is

Answer 39

10N

Question 40

A 10-N falling object encounters 10 N of air resistance. The net force on the object is

Answer 40

0N

Question 41

An apple at rest weighs 1 N. The net force on the apple when it is in free fall is

Answer 41

1N

Question 42

Whenever the net force on an object is zero, its acceleration

Answer 42

is zero

Question 43

Your car is coasting on level ground at 60 km/h and you apply the brakes until the car slows to 40 km/h. If you suddenly release the brakes now, the car tends to

Answer 43

continue moving at 40 km/h

Question 44

A 1-kg mass at the Earth's surface weighs

Answer 44

9.8 N

Question 45

A force of 1 N accelerates a mass of 1 kg at the rate of 1 m/s2. The acceleration of a mass of 2 kg acted upon by a net force of 2 N is

Answer 45

the same

Question 46

An object following a straight-line path at constant speed

Answer 46

has zero acceleration

Question 47

A push on a 1-kg brick accelerates it. Neglecting friction, to equally accelerate a 10-kg brick, one would have to push with

Answer 47

10 times as much force

Question 48

A rocket becomes progressively easier to accelerate as it travels upward from the ground mainly because

Answer 48

the mass of the rocket decreases as fuel is burned

Question 49

A rock is thrown vertically into the air. At the top of its path, its acceleration in meters per second per second is

Answer 49

9.8

Question 50

Suppose a particle is being accelerated through space by a 10-N force. Suddenly the particle encounters a second force of 10 N in the opposite direction from the first force. The particle with both forces acting on it

Answer 50

continues at the speed it had when it encountered the second force

Question 51

A 1-kg rock that weighs 9.8 N is thrown straight upward at 20 m/s. Neglecting air resistance, the net force that acts on it when it is half way to the top of its path is

Answer 51

9.8 N

Question 52

The brakes of a speeding truck are slammed on and it skids to a stop. If the truck were heavily loaded so that it had twice the total mass, the skidding distance would be

Answer 52

the same

Question 53

If an object of constant mass experiences a constant net force, it will have a constant

Answer 53

acceleration

Question 54

What horizontally-applied force will accelerate a 400-kg crate at 1 m/s2 across a factory floor against a friction force half its weight?

Answer 54

2400 N

Question 55

If less horizontal force is applied to a sliding object than is needed to maintain a constant velocity

Answer 55

the object eventually slides to a stop