physics test 2
no work is being done to hold it in place
A 500 lb steel beam is lifted up by a crane to a height of 100 ft and is held there. Part (a) How much work is being done to hold the beam in place?
50,000 lb - ft
A 500 lb steel beam is lifted up by a crane to a height of 100 ft and is held there. How much work was done to lift the beam?
50,000 lb - ft
A 500 lb steel beam is lifted up by a crane to a height of 100 ft and is held there. How much work would it take if the steel beam were raised from 100 ft to 200 ft?
7J (no nonconservative forces)
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?
Less than 7 J (due to nonconservative forces)
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?
Slightly to the left of where it was launched.
A ball is launched directly upward and ultimately reaches a height of 40 ft on a day when the wind is gusting in different directions. From the time the ball is launched until it reaches a height of 20 ft off the ground the wind is blowing at constant 20 mph to the right. From that time to the time the ball has reached the top and traveled back down to a height of 20 ft the wind is blowing at constant 20 mph to the left. As it travels from 20 ft high back to the ground the wind again blows at a constant 20 mph to the right. Where will the ball land?
mg
A ball of mass m is tossed straight up and reaches a height of 15 ft. At the top, 15 ft up, what is the magnitude of the net force on the ball?
The force of gravity exerted by the box on the Earth.
A box of mass m rests on a slope inclined by angle θ, with coefficient of static friction μ between the block and the plane.
f<mg
A box of mass m rests on a slope inclined by angle θ, with coefficient of static friction μ between the block and the plane.
mgsintheta
A box of mass m rests on a slope inclined by angle θ, with coefficient of static friction μ between the block and the plane.
f<mg
A box of mass m rests on a slope inclined by angle θ, with coefficient of static friction μ between the block and the plane. Part (a) Which of the following is true about the magnitude of the frictional force, f in relation to Fg? Choose the best answer. Assume μ is smaller than 1.
They experience the same size force.
A car and a dump truck are involved in an accident and crash into each other. Assuming the only force acting is the force of collision, which one experiences the most force during the crash - the car or the dump truck?
car
A car and a dump truck are involved in an accident and crash into each other. Which one will have the greatest magnitude of acceleration during the crash? (Assume the dump truck has a mass that is 4 times larger than the car, and the only forces in the problem are those between the two vehicles.)
gravity
A car is being lifted by a crane so that it moves upwards at a constant speed. Part (a) Which force is doing negative work on the car as it is being lifted?
gravity on the car due to earth
A car is being lifted by a crane so that it moves upwards at a constant speed. Part (a) Which force is doing negative work on the car as it is being lifted?
force of rope on car
A car is being lifted by a crane so that it moves upwards at a constant speed. Part (b) Which force is doing positive work on the car as it is being lifted?
The force of the rope acting on the car.
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?
To the right (positive x-direction).
A crate is placed on flatbed truck but is not tied down. The truck accelerates in the positive x-direction (to the right, as shown) too fast and the crate falls off the back of the truck. There is friction between the truck bed and the crate. Part (a) When the crate falls off, in what direction is it moving relative to the ground?
The friction force is in the same direction as the motion of the crate relative to the ground.
A crate is placed on flatbed truck but is not tied down. The truck accelerates in the positive x-direction (to the right, as shown) too fast and the crate falls off the back of the truck. There is friction between the truck bed and the crate. A friction force acts on the crate while it is in the truck bed. Which of the following statements is true?
no
A man pushes on a refrigerator with a force F but the refrigerator does not move. Does this force F do work?
yes
A particle is moving to the right. Part (a) Is it possible that the net force on the particle is directed to the left?
false
A particle is moving to the right. In general, the direction of the net force on a particle is always the same as the direction of its acceleration.
false
A particle is moving to the right. In general, the direction of the net force on a particle is always the same as the direction of its velocity.
yes
A particle is moving to the right. Is it possible that the net force on the particle is directed downward (perpendicular to the particle's velocity)?
At no point in the rock's trajectory is the net force equal to zero.
A rock is thrown straight upward. At which of the following points is the net force on the rock equal to zero
yes
A student is trying to push a fridge into a dorm room, but the fridge is not moving. Part (a) Is the student exerting a force on the fridge?
no
A student is trying to push a fridge into a dorm room, but the fridge is not moving. Is any power being delivered to the fridge while the student is pushing?
no
A student is trying to push a fridge into a dorm room, but the fridge is not moving.Is any work being done on the fridge?
The object will remain at the same speed, traveling in the same direction.
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 begin to move with an increasing velocity.
An object sits at rest with an unbalanced force acting on it. What do we expect this object to do?
The object will remain at rest.
An object sits at rest with no unbalanced forces acting upon it. What do we expect this object to do?
The horizontal acceleration is due only to the thrust from the jet, whereas the vertical acceleration is due to both the thrust and gravity.
Consider a jet plane, which is flying in a general direction under its own power. If we break the acceleration of this jet into two components, in the vertical and horizontal direction, what statement correctly characterizes the source of the acceleration?
2 seconds
Consider trying to lift a box tied to a rope from the ground to a first-floor window. Will it require more power to lift this box in two seconds or in two hours?
There is no energy stored in the system due to the force F.
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 rough ground with a force F over a distance d, what is the potential energy stored in the system due to this force?
gravity
Part (c) What is the Newton's third law pair to the weight of the box?
mgsin(θ)
Problem 1: A box of mass m rests on a slope inclined by angle θ, with coefficient of static friction μ between the block and the plane. Part (b) What is the magnitude of the frictional force? It is in terms of the angle θ.
There are sources of friction which we did not include in the idealized model.
When we model a pendulum, we only include the force of gravity and the force of tension on the idealized string (or other contact force which serves to change the direction of motion of the pendulum). This idealized pendulum will swing forever. In real life, pendulums eventually stop moving. Why is this?
about 100 J (9.8x1x10) mgh PEi=KEf if starting and stopping still
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. In this problem you can ignore air resistance. What is the change in the kinetic energy of the rock as it falls that distance?
centripetal force
a force that acts on a body moving in a circular path and is directed toward the center around which the body is moving.
false
a particle is moving to the right. In general, acceleration and velocity are necessarily in the same direction.
energy
ability of one system to affect the motion of another system
conservative forces
any force whose work does NOT depend on path
friction
force due to surface roughness, points parallel to surface
A body at rest will remain at rest or, if in mo tion, will remain in motion at constant velocity, unless acted on by a net external force."
newtons 1st law
The acceleration of a system is directly propor tional to and in the same direction as the net external force acting on the system and is inversely proportion to its mass."
newtons 2nd law
"Whenever one body exerts a force on a sec ond body, the first body experiences a force that is equal in magnitude and opposite in di rection to the force that it exerts."
newtons 3rd law
normal force
support force that points perpendicular to a surface
pulling force along an object, typically a string, etc.
tension
work
transfer of energy through a force
KE+PE (1/2mv^2 + mgh)
what does work equal in terms of kinetic and potential energy