PHYSICS CH 4-6
Prelecture Reading Question 5.08 Part A A 7-N vector at an angle of 45° to the horizontal has a vertical component that is about _______.
5 N
Reading Check 6.10 Part A Which undergoes the greatest change in momentum (if all of the baseballs have the same speed just before being caught and just after being thrown)?
A baseball that is caught and then thrown back
Video Tutor: Water Rocket Part A Suppose we repeat the experiment from the video, but this time we use a rocket three times as massive as the one in the video, and in place of water we use a fluid that is twice as massive (dense) as water. If the new fluid leaves the rocket at the same speed as the water in the video, what will be the ratio of the horizontal speed of our rocket to the horizontal speed of the rocket in the video after all the fluid has left the rocket? (Ignore air resistance.)
A- 2/3
Video Tutor: Weighing a Hovering Magnet Part A Consider the video tutorial you just watched. Suppose that we repeat the experiment, but this time we replace the original 56-g magnet with a more powerful magnet of the same mass. As you know from experience, the more powerful a magnet is, the more strongly it attracts or repels other magnets or magnetic objects. You have also probably noticed that magnetic forces fall off sharply with distance—two magnets that interact strongly across a distance of millimeters interact more weakly at a distance of a centimeter. (In fact, the strength of the force falls off with the square of the distance.) With the magnet hovering above the base, what will the scale read? The scale has been zeroed (tared) to subtract the weight of the base. Part B Compared to the magnet in the video, the magnet in Part A will hover at a position
A- 56 g B- farther above the base.
Video Tutor: Cart with Fan and Sail Part A Which of the force diagrams in the figure correctly displays all of the horizontal forces exerted on the cart by the surrounding air?
A- A
Think And Explain 4.77 Part A (Figure 1) The auto in the sketch moves forward as the brakes are applied. A bystander says that during the interval of braking, the auto's velocity and acceleration are in opposite directions. Do you agree or disagree?
A- Agree
Video: Acceleration Due to Gravity Part A Which ball has a greater acceleration as it drops toward the ground, and why? Part B Which ball do you predict will reach the ground first? Part C Which ball will be traveling faster when it hits the ground?
A- Ball 1 and Ball 2 have equal acceleration. B- Both Ball 1 and Ball 2 will reach the ground at the same time. C- Ball 1 and Ball 2 will be traveling equally fast when they hit the ground.
Video Tutor: Suspended Balls: Which String Breaks? Part A A heavy crate is attached to the wall by a light rope, as shown in the figure. Another rope hangs off the opposite edge of the box. If you slowly increase the force on the free rope by pulling on it in a horizontal direction, which rope will break? Ignore friction and the mass of the ropes.
A- Both ropes are equally likely to break.
Video Tutor: Happy/Sad Pendulums Part A Imagine that you replace the block in the video with a happy or sad ball identical to the one used as a pendulum, so that the sad ball strikes a sad ball and the happy ball strikes a happy ball. The target balls are free to move, and all the balls have the same mass. In the collision between the sad balls, how much of the balls' kinetic energy is dissipated? Part B Now, consider the collision between two happy balls described in Part A. How much of the balls' kinetic energy is dissipated?
A- Half of it B- None of it
Video: Friction Part A After he gets the block to move, what does Dr. Hewitt do to drag the block across the table at a steady rate? Part B If Dr. Hewitt applies 3 N of force to keep the block moving at a steady rate, what must be the force of friction, and why? Part C You are dragging a block on a surface with friction at a steady speed of 2 m/s and exert a force of 5 N to do so. What is the force of friction? Why? Part D What general rule can you conclude about the force needed to keep an object in motion at a steady rate?
A- He continues to apply a steady force. B- Equal to 3 N, because the force of friction should exactly balance out the force Dr. Hewitt applies, so that there is no net force acting on the block. C- Equal to 5 N, because the force of friction should exactly balance out the force Dr. Hewitt applies, so that there is no net force acting on the block. D- The force that you need to apply to keep an object moving at a steady rate is equal to the force resisting the motion of the object.
Interactive Figure: Newton's Second Law Part A Use the "Force applied" slider to set the force applied on the elephant to somewhere in the middle of the range. After you have set the "Force applied" slider, do not change it again for this question. How would the acceleration change if the mass of the elephant were increased? Part B Use the "Mass of elephant" slider to set the mass of the elephant to somewhere in the middle of the range. After you have set the "Mass of elephant" slider, do not change it again for this question. How would the acceleration change if the applied force on the elephant were increased?
A- It decreases. B- It increases.
Prelecture Video: Impulse and Momentum Part A In the opening scenes of the prelecture video, we outlined some of the key properties of momentum. Which of the following statements are consistent with these properties? Check all that apply. Part B Object A has a mass m and a speed v, object B has a mass m/2 and a speed 4v, and object C has a mass 3m and a speed v/3. Rank the objects according to the magnitude of their momentum. Rank from smallest to largest. To rank items as equivalent, overlap them. Part C A 1700kg rhino charges at a speed of 50.0km/h. What is the magnitude of the average force needed to bring the rhino to a stop in 0.50s? Express your answer to two significant figures. Part D A 3.6-kg chihuahua charges at a speed of 3.3m/s. What is the magnitude of the average force needed to bring the chihuahua to a stop in 0.50s? Express your answer to two significant figures. Part F Shown below is a graph of a force applied to a small object as a function of time. If the object has a mass of 5.0kg and is at rest at t=0s, how fast is the object moving at t=4.0s?
A- Momentum is a vector quantity.An object's momentum is equal to the product of its mass and its velocity. B- Object C and A the same Object B is he largest C- 4.7×104 N D- 24 N F- 7.2 m/s
Newton's Third Law Tutorial Part A The action is: Earth pulls on Moon. What is the reaction? Part B Which force is greater, the Earth's pull on the Moon, or the Moon's pull on the Earth? Part C If the cannon's recoil is the result of an equal and opposite reaction, why is the cannon's acceleration lower than the shell's acceleration? Part D Since movement of an object or system requires that a net force be applied to it, how can this occur if all action forces have opposite and equal reaction forces? Part E In Lesson 3 of the tutorial, the horse is pulling a cart. What allows the horse to accelerate forward even though the cart is pulling back on the horse? Part F Which of the following is NOT a statement or consequence of Newton's third law? Part G Which force diagram could be representing a reaction pair?
A- Moon pulls on Earth. B- Both pulls are the same. C- The cannon has more mass than the shell. D- The action force doesn't act on the same object as the reaction force. E- The force of friction the ground exerts on the horse is larger than the force the cart is pulling back on the horse. F- There can never be only one force acting on an object. G- A
Reading Check 6.19 Part A Suppose a ball of putty moving horizontally with 1 kg·m/s of momentum collides with and sticks to an identical ball of putty moving vertically with 1 kg·m/s of momentum. What is the magnitude of their combined momentum?
1.41 kg·m/s
Reading Check 4.25 Part A What is the net force that acts on a 1-kg freely falling object?
10 N
Video Tutor: Tension in String between Hanging Weights Part A Consider the video tutorial you just watched. Suppose that we duplicate this experimental setup in an elevator. What will the spring scale read if the elevator is moving upward at constant speed?
18 N
Reading Check 6.05 Part A How is the impulse -momentum relationship related to Newton's second law?
F=ma=mΔv/Δt, so Ft=Δ(mv)
Plug And Chug 4.47 Part A Using simple rearrangement of Newton's second law, show that a net force of 65 N exerted on a 13-kg package is needed to produce an acceleration of 5.0 m/s2 .
Fnet=ma=13kg⋅5.0m/s2=65N
Reading Check 5.04 Part A State Newton's third law of motion.
For every action there is an equal and opposite reaction.
Reading Check 4.17 Part A Give an example of what it means to say mass and weight are proportional to each other?
If the mass doubles, then the weight doubles, too.
Reading Check 6.02 Part A Distinguish between force and impulse.
Impulse is force times a time interval.
Reading Check 5.19 Part A Fill in the blanks: Newton's first law is often called the law of ____; Newton's second law is the law of ____; and Newton's third law is the law of ____.
Inertia, acceleration, action -reaction
Reading Check 4.14 Part A In the string-pull illustration in Figure 4.8, a sharp jerk on the bottom string results in the bottom string breaking. Does this occur because of the ball's weight or its mass?
Mass
Reading Check 4.10 Part A Fill in the blanks: The Standard International unit for mass is _____. The Standard International unit for force is _____.
Mass is kilograms; force is newtons.
Reading Check 6.16 Part A In which is momentum conserved: an elastic collision or an inelastic collision?
Momentum is conserved in elastic and inelastic collisions.
Multiple Choice Question 6.12 Part A The impulse-momentum relationship is a direct result of
Newton's 2nd law.
Multiple Choice Question 6.40 Part A The conservation of momentum is most closely related to
Newton's 3rd law.
Prelecture Reading Question 4.05 Part A The unit of mass is the kilogram, and the unit of weight is the _______.
Newton.
Reading Check 6.12 Part A Can you produce a net impulse on an automobile if you sit inside and push on the dashboard.
No never
Think And Explain 4.61 Part A Since an object weighs less on the surface of the Moon than on Earth's surface, does it have less inertia on the Moon's surface?
No.
Reading Check 4.11 Part A What is the approximate weight of a quarter-pound hamburger after it is cooked?
One newton
Reading Check 6.09 Part A Why is it advantageous to roll with the punch in boxing?
Rolling with the punch increases contact time, which decreases the force.
Think And Explain 5.70 Part A What will be the magnitude of vector S if the rope that supports Mo is vertical?
S=0
Reading Check 4.09 Part A Shake something to and fro and you're measuring its what? Lift it against gravity and you're measuring its what?
Shaking measures mass, whereas lifting measures weight.
Reading Check 6.08 Part A Why is a force that is applied for a short time more effective in karate?
The average force is increased.
Reading Check 5.02 Part A A boxer can hit a heavy bag with great force. Why can't he hit a piece of tissue paper in midair with the same amount of force?
The boxer can only hit the tissue paper with a force as large as the tissue paper can exert on the boxer, and the low-mass tissue can only exert a weak force.
Reading Check 4.30 Part A If two objects of the same size move through the air at different speeds, which encounters the greater air resistance?
The faster object encounters more air resistance.
Reading Check 4.03 Part A As you increase your push on a stationary crate, will friction on the crate increase also?
The friction force increases and is opposite in direction to your push.
Reading Check 5.16 Part A What happens to the magnitude of the normal vector on a block resting on an incline when the angle of the incline increases?
The magnitude of the normal vector decreases.
Prelecture Reading Question 5.07 Part A A Volkswagen Bug and a Volvo truck have a head-on collision. Which statement is true??
The magnitudes of both forces are the same.
Reading Check 6.01 Part A Which has a greater momentum: a heavy truck at rest or a moving skateboard?
The moving skateboard.
Reading Check 4.26 Part A What is the net force that acts on a 10-N falling object when it encounters 4 N of air resistance? When it encounters10 N of air resistance?
The net forces are 6 N and 0 N, respectively.
Reading Check 4.23 Part A The ratio circumference/diameter for all circles is π. What is the ratio force/mass for freely falling bodies?
The ratio is g.
Reading Check 4.24 Part A Why doesn't a heavy object accelerate more than a light object when both are freely falling?
The ratio of the weight to mass is the same for all objects in the same locality.
Reading Check 5.05 Part A Consider hitting a baseball with a bat. If we call the force on the bat against the ball the action force, identify the reaction force.
The reaction force is the force by the ball on the bat.
Reading Check 5.12 Part A Identify the force that propels a rocket.
The rocket is propelled by the reaction force from the particles accelerated out the rear by an action force from the rocket.
Think And Explain 4.70 Part A What happens to the weight reading on a scale you stand on when you toss a heavy object upward?
The scale reading will increase during the throw.
Reading Check 6.17 Part A Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A?
The speed of car B is equal to the initial speed of A.
Reading Check 5.18 Part A How does the magnitude of the vertical component of velocity for a ball tossed at an upward angle change as the ball travels upward? How about the horizontal component of velocity when air resistance is negligible?
The vertical component decreases in magnitude until it reaches the maximum height and then increases; the horizontal component is constant.
Prelecture Reading Question 5.01 Part A When you push against a wall, what pushes back?
The wall pushes back
Reading Check 5.03 Part A How many forces are required for an interaction?
Two forces, an action and a reaction, are needed for an interaction.
Reading Check 4.13 Part A In the string-pull illustration in Figure 4.8, a gradual pull of the lower string results in the top string breaking. Does this occur because of the ball's weight or its mass?
Weight
Prelecture Reading Question 4.04 Part A Which depends on gravity?
Weight.
Prelecture Reading Question 4.07 Part A When does the proportion form of Newton's second law take the form of an equation?
When units of newtons and kilograms are used for force and mass
Reading Check 6.13 Part A Is it correct to say that, if no net impulse is exerted on a system, then no change in the momentum of the system will occur?
Yes, always.
Reading Check 5.10 Part A Earth pulls down on you with a gravitational force that you call your weight. Do you pull up on Earth with the same amount of force?
Yes, you pull up on Earth with the same force.
Reading Check 4.04 Part A Once the crate is sliding, how hard do you push to keep it moving at constant velocity?
You push with a force equal to and opposite the dynamic friction force.
Plug And Chug 4.46 Part A Knowing that a 1-kg object weighs 10 N , select the correct equations that confirm that the acceleration of a 1-kg stone in free fall is 10 m/s2.
a=Fnetm=10N1kg=10m/s2
Multiple Choice Question 4.12 Part A Which has the greater mass?
an automobile battery
Multiple Choice Question 4.25 Part A At equilibrium on a bathroom weighting scale, the downward pull of gravity on you is balanced by
an upward support force
Multiple Choice Question 5.31 Part A When a ball falls downward, it may have a net force
any of the above
Video Tutor: Off-Center Collision Part A Suppose we replace both hover pucks with pucks that are the same size as the originals but twice as massive. Otherwise, we keep the experiment the same. Compared to the pucks in the video, this pair of pucks will rotate
at the same rate.
Reading Check 6.11 Part A In the preceding question, which case requires the greatest impulse?
baseball that is caught and then thrown back
Prelecture Reading Question 4.09 Part A As a skydiver gains speed in falling through the air, air resistance _______.
becomes negligible when terminal speed is reached.
Prelecture Reading Question 5.09 Part A When Monkey Mo dangles by a rope and pulls on his cage, each at different angle from the vertical, the rope tension will be greater than _______.
both his weight and the pull on his cage
Multiple Choice Question 5.3 Part A When you rub your hands together, you
cannot push harder on one hand than the other.
Prelecture Reading Question 6.06 Part A When a cannonball is fired from a cannon, the momentum of the recoiling cannon is momentarily _______.
equal and opposite to the momentum of the fired cannonball.
Prelecture Reading Question 6.04 Part A A boxer rides with the punch so as to reduce _______.
force
Multiple Choice Question 5.5 Part A As a ball bounces from a floor, its acceleration off the floor between bounces is
g
Prelecture Reading Question 6.03 Part A Follow through is important in golf because it results in a greater _______.
impulse on the ball.
Multiple Choice Question 6.25 Part A When a boxer moves into an oncoming punch, the force experienced is
increased.
Reading Check 6.03 Part A An impulse can be increased by
increasing the force or increasing the time interval.
Prelecture Reading Question 4.06 Part A In considering proportions, acceleration is _______.
inversely proportional to mass.
Prelecture Reading Question 4.10 Part A Air resistance on a parachutist at terminal speed _______.
is greater for a heavier person
Prelecture Reading Question 6.01 Part A A slowly moving ship can have a greater momentum than a fast-moving racing car when _______.
its mass times velocity is greater than that of the car.
Prelecture Reading Question 4.02 Part A The direction of the force of friction on a sliding crate is _______.
opposite to the direction of sliding
Prelecture Reading Question 5.05 Part A The team to win in a tug-of-war is the team that _______.
pushes harder on the floor while holding the rope
Prelecture Reading Question 5.06 Part A When hitting a tennis ball with your racquet, the force on the ball has the same magnitude as the force on the _______.
racquet
Prelecture Reading Question 5.03 Part A The force that propels a rocket is that provided by _______.
the expelled gas pushing on the rocket
Multiple Choice Question 5.10 Part A The winner in a tug-of-war exerts the greatest force on
the ground
Reading Check 6.15 Part A When a cannonball is fired, the momentum of the system (cannon + cannonball) is conserved if
the momentum of the cannon is equal to the magnitude of the momentum of the cannon ball and points in the opposite direction.
Prelecture Reading Question 4.08 Part A A 1-kg stone and a 10-kg stone have the same acceleration in free fall because _______.
the ratio of weight to mass is the same for each.
Think And Explain 6.55 Part A A lunar vehicle is tested on Earth at a speed of 10 km/h. When it travels as fast on the Moon, is its momentum more, less, or the same?
the same
Prelecture Reading Question 6.10 Part A When a falling firecracker explodes, the momenta of its pieces _______.
vectorally add up to equal the initial momentum of the firecracker
Prelecture Reading Question 4.01 Part A Whenever a net force acts on an object, there is a change in the object's _______.
velocity.
Prelecture Reading Question 6.08 Part A When two vehicles collide, momentum is conserved _______.
whether the collision is elastic or inelastic.
Think And Explain 4.81 Part A Free fall is motion in which gravity is the only force acting. Is a skydiver who has reached terminal speed in free fall? Part B Is a satellite above the atmosphere that circles Earth in free fall?
A-No. B- Yes.
Newton's Second Law Tutorial Part A Object A has three times the mass of object B. Identical forces are exerted on the two objects. Which statement is true? Part B A parachutist is falling toward the ground. The downward force of gravity is exactly equal to the upward force of air resistance. Which statement is true? Part C A kilogram is a measure of an object's __________. Part D A person who weighs 800 N (about 180 pounds) is standing on a scale inside an elevator. The elevator is moving upward yet slowing down. The reading on the scale is __________. Part E A person who weighs 800 N is squatting on a scale. Suddenly he starts jumping, extending his legs as quickly as possible, so that he can jump into the air. As the person is in the process of jumping (accelerating upward) the reading of the scale is ____________. Part F A bowling ball and a small marble will fall downward to the surface of the Moon at the same rate. Why?Part G Two identical twins are falling toward the ground. The twin in the green jumpsuit is going down head first, and the twin in the red jumpsuit is going down belly first. The two twins have the same mass. Which twin reaches the fastest terminal velocity? Part H Two parachutists have identical parachutes open and are falling toward the ground. The parachutist with the red jumpsuit is much more massive than the parachutist with the blue jumpsuit. How do the terminal velocities of the two parachutists compare?
A- The acceleration of object B is three times that of object A. B- The velocity of the parachutist is not changing with time. C- mass D- less than 800 N E- greater than 800 N F- The ratio of the force of gravity exerted on an object to the object's mass is the same. G- the twin in the green jumpsuit H- The red parachutist has a higher terminal velocity.
Think And Explain 4.58 Part A How long does that force last after the ball leaves your hand?
A- The force you exert on the ball ceases as soon as contact with your hand ceases.
Video: Action and Reaction on Rifle and Bullet Part A How does the force on the rifle compare with the force on the bullet, and why? Part B How does the magnitude of acceleration of the rifle compare with the magnitude of acceleration of the bullet, and why? Part C How does the distance traveled by the bullet compare with the distance traveled by the rifle in the same time, and why?
A- The magnitude of the force of the rifle is equal to the magnitude of force on the bullet and the forces are in the opposite direction, because for every action there is an equal and opposite reaction. B- The acceleration of the rifle is smaller than the acceleration of the bullet. They experience the same magnitude of force, but the mass of the rifle is greater, and so the rifle will experience a smaller acceleration than the bullet. C- The bullet will travel farther than the rifle because it has a greater magnitude of acceleration
Interactive Figure: Inelastic Collisions Part A Before you click "Play," predict what will happen if the red and green truck with equal mass and equal magnitude of velocity collide. Part B Predict what will happen if you reduce the magnitude of the velocity of the green truck to a magnitude smaller than that of the red truck. Part C Click "Reset." Now, predict what will happen if you change the velocity of the red truck so that it has a magnitude smaller than that of the green truck but is negative. Part D Click "Reset." Now, predict what will happen if you change the velocity of the red truck so that it has a magnitude smaller than that of the green truck but is positive. Part E Click "Reset." Now, predict what will happen if you increase the mass of the green truck so that it is greater than the mass of the red truck.
A- The trucks will stick together after the collision and not move B- The trucks will stick together after the collision and move to the left. C- The trucks will stick together after the collision and move to the right. D- The trucks will stick together after the collision and move to the right. E- The trucks will stick together after the collision and move to the right.
Think And Solve 6.37 Part A In what direction and at what speed does the wreckage move if one car was driving north and one south. Part B In what direction does the wreckage move if one car was driving north and one east (as shown in the following figure)?(Figure 1) Part C At what speed does the wreckage move if one car was driving north and one east? Express your answer to two significant figures and include the appropriate units.
A- The wreckage after collision is motionless. B- to the northeast C- v = 15/ ms
Think And Explain 5.68 Part A How does the magnitude of f relate to the vector sum of mg and N when the shoe is in equilibrium? Part B What occurs if f is less than this sum?
A- Vector f will have the same magnitude as the vector sum of mg and N. B- If f is less, then a net force acts on the shoe and it accelerates down the incline.
Think And Explain 4.60 Part A If a motorcycle moves with a constant velocity, can you conclude that there is no net force acting on it? Part B If a motorcycle moves with a constant acceleration, can you conclude that there is no net force acting on it?
A- Yes B- No
Reading Check 5.06 Part A If the system of (Figure 1) is only the orange, is there a net force on the system when the apple pulls?
A- Yes, there is the action of the apple on the orange.
Prelecture Video: Newton's Third Law Part A The video identifies the force pair produced when an apple falls through the air. Which force belongs in a free-body diagram of the apple? Part B A force pair is produced when a tennis racket strikes a tennis ball. Which of the following best explains why the tennis ball does not have zero net force acting on it? Part D What explains the dramatically different magnitudes of accelerations that result when a mosquito collides head on with a moving truck?
A- force of Earth on apple B- Each half of the force pair acts on a different object. D- unequal masses of the bus and the mosquito
Vectors Tutorial Part A The length of a force vector indicates the ________. Part B Two vectors are shown in the figure. Which of the four vectors also shown best represents the resultant vector? Part C For which situation is the tension of the ropes higher? Part D A person is hanging from two ropes, as shown in the figure. Which rope is supplying the higher tension force?
A- magnitude of force B- vector C C- case A D- The rope to the left has the higher tension.
Video: Decreasing Momentum Over a Short Time Part A How is Dr. Hewitt able to break a piece of wood in his demonstration? Part B How does Dr. Hewitt break the piece of wood? Part C What would Dr. Hewitt need to have done to exert an even greater force than he did in his karate demonstration?
A-He moves his hand very quickly. B- He causes a change in momentum of his hand over a short period of time. C- Increase the change in momentum, and decrease the time duration.
Reading Check 4.16 Part A State Newton's second law of motion.
Acceleration is proportional to net force and inversely proportional to mass.
Reading Check 4.01 Part A How does acceleration depend on the net force?
Acceleration is proportional to the net force.
