# Conceptual Questions Exam 2

question
an object sits at rest with no unbalanced forces acting upon it. what do we expect this object to do?
remain at rest
question
an object is traveling with a constant velocity with no unbalanced forces acting upon it. what do we expect this object to do?
the object will remain at the same speed, traveling in the same direction
question
an object sits at rest with an unbalanced force acting on it. what do we expect this object to do?
the object will begin to move with an increasing velocity
question
a car and a dump truck crash into each other. which one will have the greatest magnitude of acceleration during the crash?
the car
question
a car and a dump truck crash into each other. assuming the only force is the force of collision, which one experiences the most force during the crash?
they both experience the same size force
question
a ball of mass m is tossed straight up and reaches a height of 15 feet. at the top, what is the magnitude of the net force on the ball?
mg
question
a plane is flying in a general direction. if we break the acceleration of the plane into two components, in the vertical and horizontal directions, what statement characterizes the source of the acceleration?
the horizontal acceleration is due only to the thrust from the plane, while the vertical acceleration is due to both the thrust and gravity
question
a block is sitting at rest on a ramp making an incline with respect to the floor. how big is the normal force acting on the block due to the ramp?
less than mg
question
a box rests on a horizontal surface. you apply a force on the box of F = 100 N at an angle below the horizontal, and it slides at a constant velocity. the friction force that acts on the box is?
less than 100 N
question
a ball is launched directly upward and reaches a height of 40 feet. When the ball is launched until it reaches 20 feet up, the wind is blowing at a constant 20 mph to the right. From that point until the time the ball has reached the top and traveled back down to a height of 20 feet, the wind is blowing at a constant 20 mph to the left. as it travels from 20 feet high back to the ground, the wind blows at a constant 20 mph to the right. where will the ball land?
slightly to the left of where it is launched
question
a box is sitting in the back of a pickup. the pickup accelerates to the right, and because the bed of the pickup is sticky, the box does not slide around the truck when this happens. what direction is the force acting on the box due the truck?
upwards and to the right
question
a box is sitting in the back of a pickup. the pickup accelerates to the right, and because the bed of the pickup is sticky, the box does not slide around the truck when this happens. identify the forces acting on the box
static friction, gravitational force, and the normal force
question
two blocks of unequal mass are tied together with a massless string that does not stretch, and are connected via a frictionless and massless pulley. mass 1 rests on a frictionless table top. mass 2 is released and both blocks begin to move. the blocks accelerate at the same rate since they are connected. what is the acceleration?
a value between zero and g
question
a man pushes on a fridge with force F but the fridge does not move. does this force F do work?
no
question
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?
the force of gravity on the car due to earth
question
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?
the force of the rope acting on the car
question
a 500 pound steel beam is lifted up by a crane to a height of 100 feet and is held there. how much work is being done to hold the beam in place?
no work is done to hold it in place
question
a 500 pound steel beam is lifted up by a crane to a height of 100 feet and is held there. how much work was done to lift the beam?
50,000 lb-feet
question
a 500 pound steel beam is lifted up by a crane to a height of 100 feet and is held there. how much work would it take to lift the beam if it were raised from 100 feet to 200 feet?
50,000 lb-feet
question
for a conservative force, the work done against the force is transferred to the system as potential energy. if you push a wooden crate across a rough ground with a force F over a distance d, what is the potential energy stored in the system due to this force
there is no energy stored in the system due to the force F
question
a system which contains only conservative forces is an idealized version of systems found in nature, and have very special properties. if the initial energy of a conservative system is Ei and the final energy is Ef, what can we say about the relationship between these two energies in such a system?
Ei = Ef
question
a ball is dropped in a vacuum (no air resistance). as it falls it loses 7 J of potential energy how much kinetic energy did it gain?
7 J
question
a ball is dropped in the atmosphere where air resistance is present. as it falls it loses 7 J of potential energy. how much kinetic energy did it gain?
less than 7 J
question
you are holding a 1 kg rock and standing at the top of a cliff. you drop the rock off the cliff and it falls a distance 10 m. ignore air resistance. what is the change in kinetic energy of the rock as it falls that distance?
question
you stand on the edge of a tall building with three rocks, which you are going to throw off the edge. you throw the first rock straight outwards, the second at an angle of 60* above the horizontal, and the third at a angle of 30* below the horizontal. if you throw all three rocks with the same initial speed, which will be moving the fastest when it hits the ground?
they will all have the same speed
question
two objects are dropped from rest from height h. if object A is twice the mass of object B, what can be said about their kinetic energies just as they hit the ground?
object A has twice the kinetic energy of object B
question
two masses sit at the top of two frictionless inclined planes that have different angles. what can be said about the speeds of the two masses at the bottom of their respective paths?
the two balls are traveling at the same speed
question
two masses sit at the top of two frictionless inclined planes that have different angles. which mass gets to the bottom first? (M1 has a longer, less steep plane. M2 has a shorter, steeper plane)
mass 2
question
when we model a pendulum, we only include the force of gravity and the force of tension on the idealized string. this idealized pendulum will swing forever. in real life, pendulums eventually stop moving. why?
there are sources of friction which we did not include in the idealized model
question
a student is trying to push a fridge into a dorm room, but the fridge isn't moving. is the student exerting a force on the fridge?
yes
question
a student is trying to push a fridge into a dorm room, but the fridge isn't moving. is any work being done on the fridge?
no
question
a student is trying to push a fridge into a dorm room, but the fridge isn't moving. is any power being delivered to the fridge while the student is pushing?
no
question
consider trying to life a box tied to a rope from the ground to a first floor window. will it require more power to life this box in two seconds or in two hours?
two seconds
1 of 33
question
an object sits at rest with no unbalanced forces acting upon it. what do we expect this object to do?
remain at rest
question
an object is traveling with a constant velocity with no unbalanced forces acting upon it. what do we expect this object to do?
the object will remain at the same speed, traveling in the same direction
question
an object sits at rest with an unbalanced force acting on it. what do we expect this object to do?
the object will begin to move with an increasing velocity
question
a car and a dump truck crash into each other. which one will have the greatest magnitude of acceleration during the crash?
the car
question
a car and a dump truck crash into each other. assuming the only force is the force of collision, which one experiences the most force during the crash?
they both experience the same size force
question
a ball of mass m is tossed straight up and reaches a height of 15 feet. at the top, what is the magnitude of the net force on the ball?
mg
question
a plane is flying in a general direction. if we break the acceleration of the plane into two components, in the vertical and horizontal directions, what statement characterizes the source of the acceleration?
the horizontal acceleration is due only to the thrust from the plane, while the vertical acceleration is due to both the thrust and gravity
question
a block is sitting at rest on a ramp making an incline with respect to the floor. how big is the normal force acting on the block due to the ramp?
less than mg
question
a box rests on a horizontal surface. you apply a force on the box of F = 100 N at an angle below the horizontal, and it slides at a constant velocity. the friction force that acts on the box is?
less than 100 N
question
a ball is launched directly upward and reaches a height of 40 feet. When the ball is launched until it reaches 20 feet up, the wind is blowing at a constant 20 mph to the right. From that point until the time the ball has reached the top and traveled back down to a height of 20 feet, the wind is blowing at a constant 20 mph to the left. as it travels from 20 feet high back to the ground, the wind blows at a constant 20 mph to the right. where will the ball land?
slightly to the left of where it is launched
question
a box is sitting in the back of a pickup. the pickup accelerates to the right, and because the bed of the pickup is sticky, the box does not slide around the truck when this happens. what direction is the force acting on the box due the truck?
upwards and to the right
question
a box is sitting in the back of a pickup. the pickup accelerates to the right, and because the bed of the pickup is sticky, the box does not slide around the truck when this happens. identify the forces acting on the box
static friction, gravitational force, and the normal force
question
two blocks of unequal mass are tied together with a massless string that does not stretch, and are connected via a frictionless and massless pulley. mass 1 rests on a frictionless table top. mass 2 is released and both blocks begin to move. the blocks accelerate at the same rate since they are connected. what is the acceleration?
a value between zero and g
question
a man pushes on a fridge with force F but the fridge does not move. does this force F do work?
no
question
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?
the force of gravity on the car due to earth
question
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?
the force of the rope acting on the car
question
a 500 pound steel beam is lifted up by a crane to a height of 100 feet and is held there. how much work is being done to hold the beam in place?
no work is done to hold it in place
question
a 500 pound steel beam is lifted up by a crane to a height of 100 feet and is held there. how much work was done to lift the beam?
50,000 lb-feet
question
a 500 pound steel beam is lifted up by a crane to a height of 100 feet and is held there. how much work would it take to lift the beam if it were raised from 100 feet to 200 feet?
50,000 lb-feet
question
for a conservative force, the work done against the force is transferred to the system as potential energy. if you push a wooden crate across a rough ground with a force F over a distance d, what is the potential energy stored in the system due to this force
there is no energy stored in the system due to the force F
question
a system which contains only conservative forces is an idealized version of systems found in nature, and have very special properties. if the initial energy of a conservative system is Ei and the final energy is Ef, what can we say about the relationship between these two energies in such a system?
Ei = Ef
question
a ball is dropped in a vacuum (no air resistance). as it falls it loses 7 J of potential energy how much kinetic energy did it gain?
7 J
question
a ball is dropped in the atmosphere where air resistance is present. as it falls it loses 7 J of potential energy. how much kinetic energy did it gain?
less than 7 J
question
you are holding a 1 kg rock and standing at the top of a cliff. you drop the rock off the cliff and it falls a distance 10 m. ignore air resistance. what is the change in kinetic energy of the rock as it falls that distance?
question
you stand on the edge of a tall building with three rocks, which you are going to throw off the edge. you throw the first rock straight outwards, the second at an angle of 60* above the horizontal, and the third at a angle of 30* below the horizontal. if you throw all three rocks with the same initial speed, which will be moving the fastest when it hits the ground?
they will all have the same speed
question
two objects are dropped from rest from height h. if object A is twice the mass of object B, what can be said about their kinetic energies just as they hit the ground?
object A has twice the kinetic energy of object B
question
two masses sit at the top of two frictionless inclined planes that have different angles. what can be said about the speeds of the two masses at the bottom of their respective paths?
the two balls are traveling at the same speed
question
two masses sit at the top of two frictionless inclined planes that have different angles. which mass gets to the bottom first? (M1 has a longer, less steep plane. M2 has a shorter, steeper plane)
mass 2
question
when we model a pendulum, we only include the force of gravity and the force of tension on the idealized string. this idealized pendulum will swing forever. in real life, pendulums eventually stop moving. why?
there are sources of friction which we did not include in the idealized model
question
a student is trying to push a fridge into a dorm room, but the fridge isn't moving. is the student exerting a force on the fridge?