Review CH. 5-10
If the potential energy of a particle at some point in space is zero, must the force on it also be zero at that point?
no
A compressed spring is pushing a block across a rough horizontal table. Name them.
normal force, gravity, spring force, friction force
A box in the back of a truck doesn't slide as the truck stops.
not in equilibrium
A girder is being lowered into place. It is slowing down.
not in equilibrium
A stock person at the local grocery store has a job consisting of the following five segments:(1)picking up boxes of tomatoes from the stockroom floor (2)accelerating to a comfortable speed (3)carrying the boxes to the tomato display at constant speed(4)decelerating to a stop (5)lowering the boxes slowly to the floor.During which of the five segments of the job does the stock person do positive work on the boxes?
(1) and (2)
True or False: The weight of an object depends on its location.
True. The weight of an object is a measurement of how much force an object presses down on a surface with. It varies depending on location and whether the object is accelerating.
A brick is falling from the roof of a three-story building. Name them.
air drag and gravity (weight)
Suppose a highway curve is properly banked to eliminate friction for a speed of 45 mph. If your tires were bald and you wanted to avoid sliding on the road, you would have to drive
at exactly 45 mph
A 4.0-kg object is moving with speed 2.0 m/s. A 1.0-kg object is moving with speed 4.0 m/s. Both objects encounter the same constant braking force, and are brought to rest. Which object travels the greater distance before stopping?
both objects travel the same distance
A dog is standing in the bed of a pickup truck. The bed is coated with ice, causing the force of friction between the dog and the truck to be zero. The truck is initially at rest, and then accelerates to the right, moving along a flat road. As seen from a stationary observer (watching the truck move to the right), the dog
does not move left or right, but the back of the truck moves towards the dog.
An object is moving to the right, and experiencing a net force that is directed to the right. The magnitude of the force is decreasing with time. The speed of the object is
increasing
A ball drops some distance and gains 30 J of kinetic energy. Do NOT ignore air resistance. How much gravitational potential energy did the ball lose?
more than 30 J
Upon what basic quantity does kinetic energy depend?
motion
A particle moving to the left is slowed by a force pushing to the right. Is the work done on the particle positive or negative? Or is there not enough information to tell?
negative
Two men, Joel and Jerry, push against a wall. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do.
neither of them does any work
Can kinetic energy ever be negative?
no
If the force on a particle at some point in space is zero, must its potential energy also be zero at that point?
no
A process occurs in which a system's potential energy increases while the environment does work on the system. Does the system's kinetic energy increase, decrease, or stay the same? Or is there not enough information to tell?
there is not enough information
Three cars (car F, car G, and car H) are moving with the same velocity when the driver suddenly slams on the brakes, locking the wheels. The most massive car is car F, the least massive is car H, and all three cars have identical tires.(a) Which car travels the longest distance to skid to a stop?
they all travel the same distance in stopping
Swimmers at a water park have a choice of two frictionless water slides as shown in the figure. Although both slides drop over the same height, h, slide 1 is straight while slide 2 is curved, dropping quickly at first and then leveling out. How does the speed v1 of a swimmer reaching the end of slide 1 compares with v2, the speed of a swimmer reaching the end of slide 2?
v1=v2
A box slides down a frictionless plane inclined at an angle θ ¸ above the horizontal. The gravitational force on the box is directed
vertically
Can gravitational potential energy be negative?
yes
Which, if any, of the following statements concerning the work done by a conservative force is NOT true?
-It is independent of the path of the body and depends only on the starting and ending points. -When the starting and ending points are the same, the total work is zero. -It can always be expressed as the difference between the initial and final values of a potential energy function.
A box of mass m is pressed against (but is not attached to) an ideal spring of force constant k and negligible mass, compressing the spring a distance x. After it is released, the box slides up a frictionless incline as shown in the figure and eventually stops. If we repeat this experiment but instead use a spring having force constant 2k
-just as it moves free of the spring, the speed of the box will be 2√ times as great as before. -the box will go up the incline twice as high as before. -just as it moves free of the spring, the kinetic energy of the box will be twice as great as before.
A constant force applied to A causes A to accelerate at 7 m/s2. The same force applied to B causes an acceleration of 1 m/s2. Applied to C, it causes an acceleration of 8 m/s2. What is the ratio mA/mB of the mass of A to the mass of B?
1/7=0.1429
A brick is falling from the roof of a three-story building. How many force vectors would be shown on a free-body diagram?
2
An elevator suspended by a cable is descending at constant velocity. How many force vectors would be shown on a free-body diagram?
2
A compressed spring is pushing a block across a rough horizontal table. How many force vectors would be shown on a free-body diagram?
4
Two stones, one of mass m and the other of mass 2m, are thrown directly upward with the same velocity at the same time from ground level and feel no air resistance. Which statement about these stones is true?
At its highest point, the heavier stone will have twice as much gravitational potential energy as the lighter one because it is twice as heavy.
A constant force applied to A causes A to accelerate at 7 m/s2. The same force applied to B causes an acceleration of 1 m/s2. Applied to C, it causes an acceleration of 8 m/s2. Which object has the largest mass?
B
Two identical balls are thrown directly upward, ball A at speed v and ball B at speed 2v, and they feel no air resistance. Which statement about these balls is correct?
Ball B will go four times as high as ball A because it had four times the initial kinetic energy.
Block 1 and block 2 have the same mass, m, and are released from the top of two inclined planes of the same height making 30° and 60° angles with the horizontal direction, respectively. If the coefficient of friction is the same in both cases, which of the blocks is going faster when it reaches the bottom of its respective incline?
Block 2 is faster
A constant force applied to A causes A to accelerate at 7 m/s2. The same force applied to B causes an acceleration of 1 m/s2. Applied to C, it causes an acceleration of 8 m/s2. Which object has the smallest mass?
C
True or False: Mass and weight describe the same thing in different units.
False. Mass is a property of matter, and weight is a force
True or False : The mass of an object depends on its location
False. The mass of an object is a measure in which is the same regardless of location.
A mass is pressed against (but is not attached to) an ideal horizontal spring on a frictionless horizontal surface. After being released from rest, the mass acquires a maximum speed v and a maximum kinetic energy K. If instead the mass initially compresses the spring twice as far:
Its maximum speed will be 2v and its maximum kinetic energy will be 4K.
A ball tossed straight up has v=0 at its highest point. Is it in equilibrium?
No, since the ball only under the influence of gravity and has a downward acceleration
A woman is straining to lift a large crate, without success because it is too heavy. We denote the forces on the crate as follows: P is the upward force the woman exerts on the crate, C is the vertical contact force exerted on the crate by the floor, and W is the weight of the crate. How are the magnitudes of these forces related while the woman is trying unsuccessfully to lift the crate?
P+C=W
Two weights are connected by a massless wire and pulled upward with a constant speed of 1.50 m/s by a vertical pull P. The tension in the wire is T (see figure). Which one of the following relationships between T and P must be true?
P=25N + T
A box of mass m is pulled with a constant acceleration a along a horizontal frictionless floor by a wire that makes an angle of 15° above the horizontal. If T is the tension in this wire, then
T > ma
Two objects having masses m1 and m2 are connected to each other as shown in the figure and are released from rest. There is no friction on the table surface or in the pulley. The masses of the pulley and the string connecting the objects are completely negligible. What must be true about the tension T in the string just after the objects are released?
T>m2g
You toss a ball straight up in the air. Identify the agent of the force.
The agent of the gravitional force F⃗ G is the Earth and the agent of drag D⃗ is the air.
A potential energy function for system 1 is given by U1(x)=Cx2+Bx3. The potential energy function for system 2 is given by U2(x)=A+Cx2+Bx3, where A is a positive quantity. How does the force on system 1 relate to the force on system 2 at a given position?
The force is identical on the two systems.
Is the force of the mosquito on the car larger than, smaller than, or equal to the force of the car on the mosquito?
The force of the mosquito on the car is equal to the force of the car on the mosquito.
You toss a ball straight up in the air. For each force you list, state whether it is a contact force or a long-range force.
The gravitional force F⃗ G is a long-range force and the drag D⃗ is a contact force.
A 0.2 kg plastic cart and a 20 kg lead cart both roll without friction on a horizontal surface. Equal forces are used to push both carts forward a distance of 1 m, starting from rest. After traveling 1 m, is the kinetic energy of the plastic cart greater than, less than, or equal to the kinetic energy of the lead cart?
The kinetic energy of the plastic cart equal to the kinetic energy of the lead cart.
Is the magnitude of the mosquito's acceleration larger than, smaller than, or equal to the magnitude of the car's acceleration?
The magnitude of the mosquito's acceleration is larger than the magnitude of the car's acceleration. Submit
How do basketball players jump straight up into the air?
The player pushes down on the floor, which pushes back up on him. The player accelerates upward because the force of his push is greater than the force of gravity.
How does a rocket take off? What is the upward force on it?
The rocket forces the exhaust gases down, and the hot gases push up on the rocket. The two forces are a Newton's third-law pair. The rocket accelerates upward because the force of the exhaust gases on the rocket is greater than the force of gravity.
How does a sprinter sprint?
The sprinter pushes backward on the ground, which pushes back (forward) on her. This is the only horizontal force on the sprinter, so she accelerates forward.
Tarzan swings through the jungle on a massless vine. At the lowest point of his swing, is the tension in the vine greater than, less than, or equal to the gravitational force on Tarzan?
The tension in the vine is greater than the gravitational force on Tarzan.
Two objects have masses m and 5m, respectively. They both are placed side by side on a frictionless inclined plane and allowed to slide down from rest.
The two objects reach the bottom of the incline at the same time.
If the dot product of two nonzero vectors is zero, the vectors must be perpendicular to each other.
True
Two objects, each of weight W, hang vertically by spring scales as shown in the figure. The pulleys and the strings attached to the objects have negligible weight, and there is no appreciable friction in the pulleys. The reading in each scale is
W
You need to raise a heavy block by pulling it with a massless rope. You can either (a) pull the block straight up height h, or (b) pull it up a long, frictionless plane inclined at a 15∘ angle until its height has increased by h. Assume you will move the block at constant speed either way. Will you do more work in case a or case b? Or is the work the same in both cases?
Wa=Wb
Consider what happens when you jump up in the air. Which of the following is the most accurate statement?
When you push down on the earth with a force greater than your weight, the earth will push back with the same magnitude force and thus propel you into the air.
Is it possible for a system to have negative potential energy?
Yes, since the choice of the zero of potential energy is arbitrary.
You are seated in a bus and notice that a hand strap that is hanging from the ceiling hangs away from the vertical in the backward direction. From this observation, you can conclude that
You cannot conclude anything about the direction of the velocity of the bus.
A roller-coaster car rolls down a frictionless track, reaching speed v0 at the bottom. If you want the car to go twice as fast at the bottom, by what factor must you increase the height of the track?
You must increase the track height by a factor of 4. Submit
Point P in the figure indicates the position of an object traveling at constant speed clockwise around the circle. Which arrow best represent the direction the object would travel if the net external force on it were suddenly reduced to zero?
down to the right
You toss a ball straight up in the air. Immediately after you let go of it, what force or forces are acting on the ball?
drag and gravitational force
A girder is lifted at constant speed by a crane.
dynamic equilibrium
A jet plane has reached its cruising speed and altitude.
dynamic equilibrium
A fish weighing 16 N is weighed using two spring scales, each of negligible weight, as shown in the figure. What will be the readings of the scales?
each scale will read 16 N
You swing a bat and hit a heavy box with a force of 1500 N. The force the box exerts on the bat is
exactly 1500 N whether or not the box moves
A car is being towed at constant velocity on a horizontal road using a horizontal chain. The tension in the chain must be equal to the weight of the car in order to maintain constant velocity. True or false
false
If two nonzero vectors point in the same direction, their dot product must be zero.
false
If you swing a bucket of water fast enough in a vertical circle, at the highest point the water does not spill out because an outward force balances the pull of gravity on the water.
false
In order to get an object moving, you must push harder on it than it pushes back on you.
false
In order to lift a bucket of concrete, you must pull up harder on the bucket than it pulls down on you.
false
The value of the dot product of two vectors depends on the particular coordinate system being used.
false
A crate is sliding down an inclined ramp at a constant speed of 0.55 m/s. The vector sum of all the forces acting on this crate must point down the ramp.
false , the forces parallel to the motion are zero
An elevator, hanging from a single cable, moves downward and is slowing. Friction and air resistance are negligible. Is the tension in the cable greater than, less than, or equal to the gravitational force on the elevator?
greater than the gravitational force
A box of mass m is pressed against (but is not attached to) an ideal spring of force constant k and negligible mass, compressing the spring a distance x. After it is released, the box slides up a frictionless incline as shown in the figure and eventually stops. If we repeat this experiment but instead compress the spring a distance of 2x
just as it moves free of the spring, the box will be traveling twice as fast as before.
A hand presses down on a book. Is the normal force of the table on the book larger than, smaller than, or equal to mg?
larger than mg
A ball drops some distance and loses 30 J of gravitational potential energy. Do NOT ignore air resistance. How much kinetic energy did the ball gain?
less than 30 J
Two bodies P and Q on a smooth horizontal surface are connected by a light cord. The mass of P is greater than that of Q. A horizontal forceF⃗ (of magnitude F) is applied to Q as shown in the figure, accelerating the bodies to the right. The magnitude of the force exerted by the connecting cord on body P will be
less than F but not to zero
A brick is resting on a rough incline as shown in the figure. The friction force acting on the brick, along the incline, is
less than the weight of the brick
Suppose you are playing hockey on a new-age ice surface for which there is no friction between the ice and the hockey puck. You wind up and hit the puck as hard as you can. After the puck loses contact with your stick, the puck will
not slow down or speed up
Upon what basic quantity does potential energy depend?
position
An elevator held by a single cable is ascending but slowing down. Is the work done by tension positive, negative, or zero?
positive
The rope in (Figure 1) pulls the box to the left across a rough surface. Is the work done by tension positive, negative, or zero?
positive
Suppose the force of the air drag on an object is proportional to the speed of the object and in the direction opposite the object's velocity. If you throw an object upward, the magnitude of its acceleration is greatest
right after the object is released
In uniform circular motion, which of the following are constant:
speed, angular velocity, and magnitude of the net force
A compressed spring launches a block up an incline. Which objects should be included within the system in order to make an energy analysis as easy as possible?
spring, ramp, earth, and block
A 200 pound barbell is held over your head.
static equilibrium
A string is attached to the rear-view mirror of a car. A ball is hanging at the other end of the string. The car is driving around in a circle, at a constant speed. Which of the following lists gives all of the forces directly acting on the ball?
tension and gravity
An elevator suspended by a cable is descending at constant velocity. Name them.
tension and gravity
(Figure 1) shows a hollow tube forming three-quarters of a circle. It is lying flat on a table. A ball is shot through the tube at high speed. As the ball emerges from the other end, does it follow path A, path B, or path C?
the ball follows path C
Suppose you attempt to pour out 100 g of salt, using a pan balance for measurements, while an elevator that is accelerating upward. Will the quantity (weight) of salt be too much, too little, or the correct amount?
the correct amount
When a parachutist jumps from an airplane, he eventually reaches a constant speed, called the terminal speed. Once he has reached terminal speed
the force of air drag on him is equal to his weight.
A 20-ton truck collides with a 1500-lb car and causes a lot of damage to the car. During the collision:
the force of on the truck due to the collision is exactly equal to the force on the car.
A crate of fragile dishes is in the back of a pickup truck. The truck accelerates north from a stop sign, and the crate moves without slipping. Does the friction force on the crate point north or south? Or is the friction force zero?
the friction force on the crate points north
Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. When they hit the ground
the heavier one will have twice the kinetic energy of the lighter one.
A box of mass m is pressed against (but is not attached to) an ideal spring of force constant k and negligible mass, compressing the spring a distance x. After it is released, the box slides up a frictionless incline as shown in the figure and eventually stops. If we repeat this experiment with a box of mass 2m
the lighter box will go twice as high up the incline as the heavier box.
An object is moving forward with a constant velocity. Which statement about this object MUST be true?
the net force on the object is zero
Consider a plot of the displacement (x) as a function of the applied force (F) for an ideal elastic spring. The slope of the curve would be
the reciprocal of the spring constant.
A girl throws a stone from a bridge. Consider the following ways she might throw the stone. The speed of the stone as it leaves her hand is the same in each case, and air resistance is negligible.Case A: Thrown straight up.Case B: Thrown straight down.Case C: Thrown out at an angle of 45° above horizontal.Case D: Thrown straight out horizontally.In which case will the speed of the stone be greatest when it hits the water below?
the speed will the same in all cases
A ball is tossed vertically upward. When it reaches its highest point (before falling back downward)
the velocity is zero, the acceleration is directed downward, and the force of gravity acting on the ball is directed downward.
A 3.00-kg ball swings rapidly in a complete vertical circle of radius 2.00 m by a light string that is fixed at one end. The ball moves so fast that the string is always taut and perpendicular to the velocity of the ball. As the ball swings from its lowest point to its highest point
the work done on it by gravity is -118 J and the work done on it by the tension in the string is zero.
If a force always acts perpendicular to an object's direction of motion, that force cannot change the object's kinetic energy.
true
When an object is solely under the influence of conservative forces, the sum of its kinetic and potential energies does not change.
true
Suppose you press your physics book against a wall hard enough to keep it from moving. Does the friction force on the book point into the wall, out of the wall, up, down, or is there no friction force?
up
A sprinter accelerates from rest. Is the work done on the sprinter positive, negative, or zero?
zero
A stalled car is being pushed up a hill at constant velocity by three people. The net force on the car is
zero
A particle moves in a vertical plane along the closed path seen in (Figure 1) starting at A and eventually returning to its starting point. Is the work done by gravity positive, negative, or zero?
zero because total displacement is zero