PHYS 11A Sac State fall19
Determine the number of significant figures for the value 7,790,200
5
A pendulum bob with a weight of 4.0 N is held at an angle θ from the vertical by a horizontal force F as shown. The tension in the string supporting the ball is 6.0 N. The horizontal force F must be _______ N (Enter ONLY the number (without the N))
Answer 4.47
Consider a person standing in an elevator that is accelerating upward. The upward normal force N exerted by the elevator floor on the person is A. larger than B. identical to C. smaller than D. the downward weight W of the person.
Answer: A In order for the person to be accelerated upward, the normal force exerted by the elevator floor on her must exceed her weight.
Consider two objects A & B, launched at the same time, following the below paths: Which object hits the ground first? A. A B. B C. They hit at the same time D. Not enough information to know
Answer: B For time in the air, all that matters is the vertical motion. A goes higher, so takes more time (think: in y motion, they both start from rest at their peak; A has farther to go so is in the air longer)
An elevator decelerates to a stop while moving upwards. If you (mass = mp) stand on a scale inside that elevator it would show your weight as... A. greater than mpg B. less than mpg C. equal to mpg D. zero
Answer: B In this case the acceleration is decreasing, meaning that in order to make the elevator come to a stop the acceleration needs to act in the opposite direction, -j^ , this makes the acceleration negative.
A ball tossed vertically upward rises, reaches its highest point, and then falls back to its starting point. During this time the acceleration of the ball is always A. in the direction of motion. B. directed downward. C. directed upward. D. opposite its velocity. E. none of the above
Answer: B directed downward.
Five coconuts are thrown in five different directions from the top of a coconut tree. Each coconut has an initial speed of 8 m/s and later lands on the level ground. The five directions are 1) Straight up 2) 45° above horizontal 3) Horizontal 4) 45° below horizontal 5) Straight down Which of the following is the correct ranking for the final speed of the coconuts (when each is about to hit the ground)? A. 1 > 2 > 3 > 4 > 5 B. 1 = 5 > 2 = 4 > 3 C. 1 = 2 = 3 = 4 = 5 D. 1 > 4 > 3 > 2 > 1 E. 5 > 4 > 3 > 2 > 1
Answer: C 1 = 2 = 3 = 4 = 5
A box of mass m is hung with a string from the ceiling of an elevator that is accelerating upward. Which of the following best describes the tension in the string? A. mg > T B. T = mg C. T > mg
Answer: C T > mg
A spring has a spring constant of 100 N/m. How much potential energy does it store when stretched by 10 cm? A. 50 J B. 10 J C. 5.0 J D. 0.50 J E. 0.10 J
Answer: D 0.50 J
If you push twice as hard against a stationary wall, the amount of work you do on the wall A. doubles B. remains constant but non-zero C. remains constant and zero D. is halved
Answer:C
How many significant figures does the following number have? 0.03020
4 The zeroes before the 3 are not significant, but all other digits (3020) are significant, giving a total of 4 significant figures.
The Grinch has a heart that is two sizes too small. If the Grinch's heart pumps 3 liters of blood per minute [L/min], what is this rate in unit of cubic inches per second [in3/s]? There are 1000 mL in 1 L. There is 1 cubic centimeter in 1 mL. There are 2.54 cm in 1 inch. A. 3.05 in3 / s B. 3.05 x 10-3 in3 / s C. 0.328 in3 / s D. 820 in3 / s
A. 3.05 in3 / s
The following system is held in equilibrium by the mass supported at A and the angle θ of the connecting cord. Draw the free-body diagram for the connecting knot D. The knot at D is subjected to three external forces. Match the external force with the weight that it is caused by:
Answer Force in direction from D to E - Weight C Force in direction from D to F - Weight A Force in the direction from D to B - Weight B
A 2.0 kg block is moving at 10 m/s along a horizontal frictionless table. It encounters and compresses a spring whose other end is attached to a wall. How much potential energy is stored in the spring at the moment when the block stops moving? (Do not include units in your answer.)
Answer 100
Shown above are six velocity-time graphs for toy robots that are traveling along a straight course. All robots are initially facing the same way. All graphs have the same time and velocity scale. Rank these situations on the basis of the displacement (where the largest negative displacement is the "least" and the largest positive displacement is the "greatest"). A B C D E F
Answer A < C < E < F < B < D since these are velocity versus time graphs the displacements are given by the areas "under" (between the lines and the time axis) the lines in the graphs.
Boxes are pulled by ropes along frictionless surfaces, accelerating toward the left. All of the boxes are identical, and the accelerations of all three systems are the same. Rank the tensions in the ropes. A. A B. B C. C D. D E. E F. F
Answer A = C = F < E = B < D Since the boxes all have the same mass (m) and all of the accelerations are the same, the tensions will be determined by how many boxes the rope is accelerating. The only horizontal force on the rightmost blocks in each case is the tension in the rope to the left of that block (A, C, and F), and this tension must therefore be the mass of that block times the acceleration, ma. The tension in ropes B and E are the net forces on the systems of the two blocks to their right, so the tensions in these ropes must be 2ma. For the system of all 3 blocks in the last case the net force is the tension in rope D, 3ma.
Which of the following should be included when considering the total mechanical energy of a system? Pick all which apply. A. Kinetic energy B. Gravitational potential energy C. Spring energy D. Energy converted to sound E. Energy converted to heat F. Work done by friction
Answer A, B, and C
A geeky ice skater is holding a heavy mass in each hand. Holding both arms out, she goes into a slow spin. As she pulls each mass closer by about 0.5 meters (pull: another word for force), she spins at an incredible speed. Which of the following are true? Select all that apply. A. Her moment of inertia decreased B. Her angular velocity stayed the same C. Her muscles perform positive work when she pulls in the masses D. Her rotational kinetic energy does not change E. There is a net torque on the ice skater F. Her angular momentum does not change
Answer A, C, and F Is energy conserved as she pulls her hands closer? Well, is there any work done by a force that isn't accounted for in the potential energy? Yes! She must perform work to move the masses closer a certain distance. The work-energy theorem is still valid, K1+U1+Wother=K2+U2K1+U1+Wother=K2+U2 It's just that you'll probably have trouble calculating WotherWother unless that is the only unknown. Instead, think about angular momentum. Is there a net torque on the skater? No, and she can't possibly exert a net torque on herself. Therefore, there is no change in angular momentum. ∑τ⃗ =dL⃗ dt∑τ→=dL→dt
A DVD is rotating with an ever-increasing speed. The point P is close to the axis of rotation, and the point Q is close to the rim of the DVD. How do the centripetal acceleration a(rad) and tangential acceleration a(tan) compare at points P and Q? A. P and Q have the same a(rad) and a(tan). B. Q has a greater a(rad) and a greater a(tan) than P. C. Q has a smaller a(rad) and a greater a(tan) than P D. Q has a greater a(rad) and a smaller a(tan) than P. E. P and Q have the same a(rad), but Q has a greater a(tan) than P
Answer B a(tan) = rω a(rad) = v2/r = (ωr)2/r = rω2 Both P and Q have the same angular velocity, so both a(tan) and a(rad) are larger are larger radius
Boxes A and B are being pulled to the right on a frictionless surface; the boxes are speeding up. Box A has a larger mass than Box B. How do the two tension forces compare? A. T1 > T2 B. T1 = T2 C. T2 > T1 D. Not enough information to tell
Answer C T2 needs to be able to pull both blocks, T1 need only pull block A
Two stones are dropped into a bottomless pit. The second stone is dropped two seconds after the first stone. Assume no air resistance. As both stones fall, the difference in their velocities A. increases B. decreases C. remains constant
Answer C remains constant
Tuna Hockey Part 3: A hockey puck (m = 0.300 kg) sliding at 15 m/s across slippery ice strikes a can of tuna ( m = 0.400 kg) initially at rest and continues on at an angle of 25.0 degrees to its initial line of motion. The dented tuna can moves off at an angle of 40.0 degrees as shown. What is the final speed of the hockey puck, in units of m/s (do not include the units)?
Answer: 10.32 Both the x and y components of momentum remain constant, so that gives 2 equations for 2 unknowns. The algebra is a bit tricky, though...
A car engine is suspended from a chain linked at O to two other chains. Which of the following forces should be included in the free-body diagram for the engine? A. tension T1 B. tension T2 C. tension T3 D. two of the above E. T1, T2, and T3
Answer: A
Two blocks with the same mass are connected by a lightweight cord that runs through an ideal pulley. They are held in the positions shown. When released, the blocks will end up A. at their current heights. B. at the same height. C. with block 1 on the ground. F. with block 2 on the ground.
Answer: A
A small ball rolls including friction along a loop-the-loop starting from rest at height, h_initial. What is the height, h_loop, at the top of the loop-the-loop, assuming contact is maintained throughout the loop? A. h_initial > h_loop B. h_loop =h_initial C. h_loop > h_initial D. Not enough information
Answer: A h_initial > h_loop
A mass m accelerates downward along a frictionless inclined plane. The magnitudes of the forces on the free-body diagram have not been drawn carefully, but the directions of the forces are correct. Which statement below is true? A. mg > N B. N > mg C. N = mg
Answer: A mg > N
An object is being acted upon by three forces and as a result moves with a constant velocity. One force is 60.0 N along the +x-axis, and the second is 75.0 N along the +y-axis. What is the magnitude of the third force? A. 96.0 N B. 135 N C. 67.5 N D. 15.0 N E. 48.0 N
Answer: A 96.0 N
Two balls of equal mass are thrown horizontally with the same initial velocity. They hit identical stationary boxes resting on a frictionless horizontal surface. The ball hitting box 1 bounces back, while the ball hitting box 2 gets stuck. Which box ends up moving faster after the collision? A. Box 1 B. Box 2 C. Same
Answer: A Box 1
A car rolls up an inclined ramp, stops, then rolls back down. Assume up is the positive direction. At the moment that the car is stopped, what is the net force acting on the car? A. Constant and downward B. Increasing and downward C. Decreasing and downward Zero E. Decreasing and upward F. Constant and upward G. Increasing and upward
Answer: A Constant and downward
When a dish falls, will the change in momentum be less if it lands on a carpet than if it lands on a hard floor? (Careful!) A. No, both are the same. B. Yes, less if it lands on the carpet. C. No, less if it lands on a hard floor. D. No, more if it lands on a hard floor.
Answer: A Explanation: The momentum becomes zero in both cases, so both change by the same amount. Although the momentum change and impulse are the same, the force is less when the time of momentum change is extended. Be careful to distinguish among force, impulse, and momentum.
Which of the following statements is true about the total mechanical energy of a system? A. It is constant if acted upon by a conservative force B. It is constant if acted upon by a non-conservative force C. It is always positive D. It is equally divided between its kinetic energy and potential energy
Answer: A It is constant if acted upon by a conservative force
Must a car with momentum have kinetic energy? A. Yes, due to motion alone B. Yes, when motion is nonaccelerated C. Yes, because speed is a scalar and velocity is a vector quantity D. No
Answer: A Speed being a scalar, and velocity being a vector quantity are irrelevant. Any moving object has both momentum and kinetic energy.
A person pulls a box along the ground at a constant speed. If we consider Earth and the box as our system, the work done by the person on the system is A. positive. B. zero. C. negative.
Answer: A The person exerts a force on the box (via the rope) toward the right. The work (due to the rope) is then equal to this force times the distance traveled. Since these two quantities are both positive (both in the same direction), the work will be positive. Note that the vector sum of the forces on the box is zero, since it moves at constant velocity. The additional force is due to friction from the earth, pushing in the direction opposite to the motion and equal in magnitude to the tension in the rope.
Tuna Hockey Part 2: A hockey puck (m = 0.300 kg) sliding at 15 m/s across slippery ice strikes a can of tuna ( m = 0.400 kg) initially at rest and continues on at an angle of 25.0 degrees to its initial line of motion. The dented tuna can moves off at an angle of 40.0 degrees as shown. For the puck-can system, during which portion of the motion does momentum remain constant? A. The entire motion. B. From the start to just before the collision. C. From just after the collision to the end. D. At all times except during the collision. E. None of these.
Answer: A The puck-can system seems to be isolated from external forces, so there is nothing to change the momentum of the system, even during the collision.
An object hangs motionless from a spring. Think about the sum of the elastic potential energy of the spring and the gravitational potential energy of the object and Earth (Uspr+Ug)(Uspr+Ug). When the object is pulled down and held, this sum A. increases. B. stays the same. C. decreases.
Answer: A increases
A small mass m on a string is rotating without friction in a circle. The string is shortened by pulling it through the axis of rotation without any external torque, what happens to the angular velocity of the object? A. It increases B.It decreases C. It remains the same
Answer: A it increases
Signs are suspended from equal-length rods on the side of a building. For each case, the mass of the sign compared to the mass of the rod is small. The mass of the sign is given in each figure. In Cases B and D, the rod is horizontal; in the other cases, the angle that the rod makes with the vertical is given.Rank the magnitude of the torque the signs exert about the point at which the rod is attached to the side of the building. A. A B. B C. C D. D
Answer: A < C < D < B B is first, then D, C, and finally A. Explanation: The torque depends on the weight of the sign (mg) times the distance from the line of action of this weight to the point of attachment
Forces of 2 N and 8 N act at a point. Which of the following could not be the magnitude of their resultant? Choose all that apply. A. 12 N B. 5 N C. 8 N D. 7 N
Answer: A and B 12N & 5N
Suppose you have a spring attached on one side to a wall. According to Hooke's law, the force exerted by a spring is: A. proportional to the displacement respect to the equilibrium position B. proportional to the distance of the end of the spring respect to the wall C. always pushing away from the equilibrium position D. always pushing towards the equilibrium position E. always pushing towards the wall F. always pushing away from the wall G. dependent on the material of the spring
Answer: A, D, and G The force of a spring is a restoring force, it always wants to push back the spring to its relaxed/equilibrium position, therefore it will push towards the wall if you extend it, and away from the wall if you compress it. F=−kΔxF=−kΔx The magnitude of the force only depends on the displacement ΔxΔx from the equilibrium position, more you pull/push the spring away from equilibrium stronger it will be the force. The force does not depend on the physical lenght of the spring. The spring constant k characterizes how strong is the restoring force and depends on the material/kind of spring. A small k will define a "soft" spring, that can be pushed/pulled with a little force, a big k will define a "hard" spring, that requires a big force to be extended/compressed from equilibrium.
A fellow student spins a ball on a string over the head (like a helicopter). The ball undergoes uniform circular motion in a vertical plane. The string breaks at the moment shown below. Which picture most correctly depicts the subsequent motion of the ball? A.A B. B C. C D. D
Answer: B The ball's velocity at any moment is tangent to the circular path it follows. When the string is broken, the ball will move in a straight line, with an initial velocity tangent to the circle.
A crate is moving to the right on a conveyor belt without slipping. The conveyor belt has been running for a while and maintains a constant speed. The force of friction on the crate is A. to the right B. zero C. to the left
Answer: B The crate is not accelerating, so there is no net force needed to keep it going. It wouldn't slide against the conveyor belt even if it could, so friction does not need to do anything.
A train car moves along a long straight track. The graph shows the position as a function of time for this train. The graph shows that the train: speeds up all the time. slows down all the time. speeds up part of the time and slows down part of the time. moves at a constant velocity.
Answer: B The slope of the curve diminishes as time increases.
If you drop an object in the absence of air resistance, it accelerates downward at 9.8 m/s2 after you let it go. If instead you throw it downward, its acceleration after release is A. less than 9.8 m/s2. B. 9.8 m/s2. C. more than 9.8 m/s2.
Answer: B 9.8 m/s2.
You are trying to open a door that is stuck by pulling on the doorknob in a direction perpendicular to the door. If you instead tie a rope to the doorknob and then pull with the same force, is the torque you exert increased? A. yes B. no
Answer: B Because the force you are applying is unchanged and the perpendicular distance between the line of action and the pivot point (the lever arm) is likewise unchanged, the torque you apply does not increase. (Pulling at an angle only decreases the lever arm.)
A fast-moving car coming to rest after hitting a haystack or a cement wall produces vastly different results.1. Do both experience the same change in momentum?2. Do both experience the same impulse?3. Do both experience the same force? A. Yes for all three B. Yes for 1 and 2 C. No for all three D. No for 1 and 2
Answer: B Explanation:Although stopping the momentum is the same whether done slowly or quickly, the force is vastly different. Be sure to distinguish among momentum, impulse, and force.
What can we say about the skater's initial and final rotational kinetic energies? A. Final Krot= Initial Krot B. Final Krot > Initial Krot, because of larger ω C. Initial Krot > Final Krot, because of smaller I
Answer: B Final Krot > Initial Krot, because of larger ω
A bobsledder pushes her sled across horizontal snow to get it going, then jumps in. After she jumps in, the sled continues at a constant velocity. What forces act on the sled just after she's jumped in? A. Gravity and kinetic friction B. Gravity and a normal force C. Gravity and the force of the push D. Gravity, a normal force, and kinetic friction E. Gravity, a normal force, kinetic friction, and the force of the push
Answer: B Gravity and a normal force
A block slides on ice. The ice is banked, so the block slides around in a horizontal circle. What direction is the net force? A. Vertical B. Horizontal C. Uphill D. Downhill
Answer: B Horizontal
A pumpkin attached to a string is moving on a circular trajectory with contstant speed. The acceleration points towards the center of the circle. In which direction does the net force act on the pumpkin? A. In the direction of the velocity B. In the direction of the acceleration (towards the center of the circle) C. The net force is zero since the magnitude of the velocity is constant
Answer: B In the direction of the acceleration (towards the center of the circle)
In the following figure, a 10-kg weight is suspended from the ceiling by a spring. The weight-spring system is at equilibrium with the bottom of the weight about 1 m above the floor. The spring is then stretched until the weight is just above the eggs. When the spring is released, the weight is pulled up by the contracting spring and then falls back down under the influence of gravity. On the way down, it A. reverses its direction of travel well above the eggs. B. reverses its direction of travel precisely as it reaches the eggs. C. makes a mess as it crashes into the eggs.
Answer: B In the initial situation, with the spring stretched until the bottom of the weight is just above the eggs, all of the energy of the system is potential. Upon release, some of this energy is converted to kinetic energy in the moving spring and weight. When the weight returns to its position just above the eggs, however, all of the energy in the system must again be potential. Having no kinetic energy, the weight stops at the point from which it was initially released. The eggs are safe.
Two marbles, one twice as heavy as the other, are dropped to the ground from the roof of a building. Just before hitting the ground, the heavier marble has A. as much kinetic energy as the lighter one. B. twice as much kinetic energy as the lighter one. C. half as much kinetic energy as the lighter one. D. four times as much kinetic energy as the lighter one. E. impossible to determine
Answer: B Kinetic energy is proportional to mass, and we also know that both marbles have the same velocity.
An object moves at constant speed along the path pictured at right. At which of A, C or E (if any) is its acceleration zero? A. At A only B. At C only C. At E only D. Everywhere (constant speed) E. None of the above
Answer: B No acceleration means no change in velocity. We already know the speed is constant, but if the direction of motion is changing then that will also require acceleration
In what form is the energy stored in the initial state of the dart gun? A. Kinetic energy B. Potential energy C. Kinetic and potential energies D. None
Answer: B Potential energy
A block having mass m slides on a frictionless surface and runs into a block of mass M which is initially at rest. The blocks stick together and their speed after the collision is half the speed the moving block had before the collision. How do the masses of the blocks compare? A. M>m B. m=M C. m>M
Answer: B Since there are no external forces, we impose conservation of the total momentum before and after the collision: mv=(m+M)vfmv=(m+M)vf therefore vf=mm+Mvvf=mm+Mv We know vf=v2vf=v2 and therefore this is true if mm+M=12→m=M
On a carousel (merry-go-round), if you sit on one of the horses close to the center, you will experience a greater or smaller centripetal acceleration than if you would sit on one of the horses near the outer edge? A. greater B. smaller
Answer: B Smaller
A rope is wound around a large solid disk as shown, the rope is then connected to a block that is pulled along the frictionless table by a force F. What do the disk and the block have in common? A. The block's acceleration is equal to the disk's radial acceleration. B. The block's acceleration is equal to the disk's tangential acceleration. C. The block's acceleration is equal to the disk's angular acceleration.
Answer: B The block's acceleration is equal to the disk's tangential acceleration.
You hold one end of a meter stick between the fingers of one hand and let it fall from its initial almost vertical position as shown below. Consider the torque due to gravity around the fixed end (pivot point) of the meter stick. When is the magnitude of this torque greatest? A. A B. B C. C D. D E. E F. The torque is always the same.
Answer: B The force of gravity can be considered to act at the stick's center of mass and always points down. Thus the maximum lever arm for this force occurs when the meter stick is horizontal (as in B).
A 2 gram bullet moving at around 300 m/s horizontally hits a 2kg block suspended vertically by wires. During the collision A. Energy is conserved B. Momentum is conserved C. Both energy and momentum are conserved D. Neither energy nor momentum is conserved
Answer: B The vertical wires can exert no force in the horizontal direction, so horizontal momentum is conserved in this collision
Suppose you are on a cart, initially at rest on a track with very little friction. You throw balls at a partition that is rigidly mounted on the cart. If the balls bounce straight back as shown in the figure, is the cart put in motion? A. Yes, to the right. B. Yes, to the left. C. No, it stays in place.
Answer: B Yes, to the left.
Suppose you double the speed at which you round a bend in the curve, by what factor must the centripetal force change to prevent you from skidding? A. Double B. Four times C. Half D. One-quarter
Answer: B a=v2/r Because the term for "tangential speed" is squared, if you double the tangential speed, the centripetal force will be double squared, which is four times.
A ball is released from rest on a no-slip surface, as shown. After reaching its lowest point, the ball begins to rise again, this time on a frictionless surface as shown in the figure. When the ball reaches its maximum height on the frictionless surface, it is: A. at a greater height than when it was released B. at a lower height than when it was released C. at the same height as when it was released
Answer: B at a lower height than when it was released
Two vehicles with equal magnitudes of momentum traveling at right angles to each other undergo an inelastic collision. The magnitude of momentum for the combined wreck is A. less than the magnitude of momentum of either car before collision. B. greater than the magnitude of momentum of either car before collision. C. the same as the magnitude of momentum of either car before collision. D. none of the above
Answer: B greater than the magnitude of momentum of either car before collision.
The red ball is dropped while the yellow ball has an initial velocity pointing right (horizontally). Which ball has the greater velocity at ground level? A. the "dropped" ball B. the "fired" ball C. neither—they both have the same velocity on impact D. it depends on how hard the ball was thrown
Answer: B the "fired" ball
A ball rolling down an incline has its maximum kinetic energy at A. halfway down. B. the bottom. C. three-quarters of the way down. D. the top.
Answer: B the bottom.
You are walking on a level floor. You are getting good traction, so the soles of your shoes don't slip on the floor. Which of the following forces should be included in a free-body diagram for your body? A. the force of kinetic friction that the floor exerts on your shoes B. the force of static friction that the floor exerts on your shoes C. the force of kinetic friction that your shoes exert on the floor D. the force of static friction that your shoes exert on the floor E. more than one of these
Answer: B the force of static friction that the floor exerts on your shoes
Which among the following are conservative forces: A. friction B. elastic (force of a spring) C. tension D. air resistance E. gravity
Answer: B and E elastic (force of a spring) & gravity
A car rolls up an inclined ramp, stops, then rolls back down. Assume up is the positive direction. At the moment that the car is stopped, what is its instantaneous acceleration? A. positive B. zero C. negative
Answer: C
Angular acceleration, α, is related to the net torque, τnet, by a relationship based on Newton's second law for rotational motion, τnet=Iατnet=Iα. Which of the object's below experiences the smallest angular acceleration? A. a B. b C. c D. More than one of these options are correct
Answer: C
Consider the object below. A long rectangular block has had one square piece removed from it. Roughly, which of the five locations indicated is closest to the center of mass of the new object? A. A B. B C. C D. D E. E
Answer: C
You stop a friend who is riding a bicycle by pushing against the handlebars. If the kinetic energy of your friend (and the bicycle) is equal to K, the work you do on your friend is: A. equal to K B. zero C. equal to -K D. cannot be calculated from what is given
Answer: C
A fellow student spins a ball on a string in front of them. The ball undergoes uniform circular motion in a vertical plane. The string breaks at the moment shown below. Which picture most correctly depicts the subsequent motion of the ball? A. A B. B C. C D. D
Answer: C The ball's velocity at any moment is tangent to the circular path it follows. When the string is broken, the ball will move in projectile motion under only the influence of gravity, with an initial velocity tangent to the circle. Thus the ball will describe the parabolic arc shown in C.
The graph shows position as a function of time for two trains running on parallel tracks. Which is true: A. At time t_b, both trains have the same velocity. B. Both trains speed up all the time. C. Both trains have the same velocity at some time before tBtB. D. At some instant, both trains have the same acceleration. E. None of the above statements is true
Answer: C The slope of curve B is parallel to line A at some instant t<tB.
You drop a ball from rest and simultaneously shoot a second, identical ball horizontally from the same height as the first ball. If there is no air resistance, which ball hits the ground first? A. The dropped ball hits first. B. The ball shot horizontally hits first. C. They both hit at the same time. D. Answer depends on the speed with which the second ball is shot. E. Answer depends on the speed with which the second ball is shot and the masses of the balls.
Answer: C They both hit at the same time.
For general projectile motion, when the projectile is at the highest point of its trajectory A. its acceleration is zero B. the horizontal and vertical components of its velocity are zero. C. its velocity is perpendicular to the acceleration . D. its velocity and acceleration are both zero
Answer: C its velocity is perpendicular to the acceleration .
The top block is accelerated across a frictionless table by the falling mass m. The string is massless, and the pulley is both massless and frictionless. The tension in the string is A. T>mgT>mg B. T=mgT=mg C. mg>T
Answer: C mg>T
A spring-loaded gun shoots a plastic ball with a launch speed of 2.0 m/s. If the spring is replaced with a new spring having twice the spring constant (but still compressed the same distance), the ball's launch speed will be A. 1.0 m/s B. 2.0 m/s C. 2.8 m/s D. 4.0 m/s E. 16.0 m/s
Answer: C 2.8 m/s
What does the scale read? Answering this requires reasoning, not calculating. A. 500 N B. 1000 N C. 2000 N D. 4000 N
Answer: C 2000 N
At t = 0, a ball, initially at rest, starts to roll down a ramp with a constant acceleration. Suppose it moves 1 foot between t = 0 s and t = 1 s. How far does it move between t = 1 s and t = 2 s? A. 1 ft B. 2 ft C. 3 ft D. 4 ft E. 6 ft
Answer: C 3 ft
A compact car and a large truck collide head-on and stick together. Which undergoes the larger momentum change? A. Car B. Truck C. The momentum change is the same for D. both vehicles E. Can't tell without knowing the final velocity of combined mass
Answer: C Conservation of momentum tells us that the changes in momentum must add up to zero. So the change in the car's momentum must be equal to the change in the truck's momentum, and the two changes must be in the opposite directions.
A bicyclist is riding at constant speed along a straight path. The rider throws a ball straight up to a height of a few meters above her head. Ignoring air resistance, where will the ball land? A. Ahead of the rider B. Behind the rider C. Directly back in the hand that threw it D. Depends on the maximum height the ball reaches
Answer: C Directly back in the hand that threw it
Suppose by pulling the weights inward, the rotational inertia of the man reduces to half its value. By what factor would his angular velocity change? A. Half B. Four times C. Double D. One-quarter
Answer: C Double
Two toy trucks travelling at different constant speeds are about to collide. The two identical trucks are traveling in opposite directions, and truck A is carrying a heavy load.During the collision, will the magnitude of the force exerted on truck A by truck B be _____ the magnitude of the force exerted on truck B by truck A? A. greater than B. less than C. equal to
Answer: C Explanation: These are all Newton's Third Law pairs of forces, so they have to be equal.
A croquet mallet balances when suspended from its center of mass, as shown in the left part of the figure. If you cut the mallet into two pieces at its center of mass, as shown in the right part of the figure, how do the masses of the two pieces compare? A. The masses are equal. B. The piece with the head of the mallet has the smaller mass. C. The piece with the head of the mallet has the greater mass. D. It is impossible to tell.
Answer: C For the mallet to balance at the point shown, the torque due to gravity on each side of the center must be zero. Since the mass on the "head" side is closer to the balance point, the force at that point must be bigger to compensate (since torque is the product of force and distance to the rotation axis).
Now suppose you throw a ball oFf putty at the wall, and instead of rebounding it sticks (in a fully inelastic collision). In this case is the cart moving after the collision? A. Yes, to the right. C. Yes, to the left. D. No, it stays in place.
Answer: C No, it stays in place.
The three objects below all have the same mass and each has a uniform density. They rotate about a vertical axis through their center of mass, as shown by the dotted lines. Rank them in order from SMALLEST moment of inertia (at left) to LARGEST moment of inertia (at right). A. A,B,C B. A,C,B C. B,A,C D. B,C,A E. C,A,B F. C,B,A
Answer: C Object B has the most mass near the center and away from the edges. Object A has slightly more mass at a distance from the axis of rotation. Object C has the most mass far from the axis of rotation. Since moment of inertia is proportional to the distance from the axis squared, the correct ranking is B,A,C
When an ice skater is spinning and pulls in her arms, her angular velocity (blank) because her (blank). A.increases; mass decreases B. decreases; moment of inertia increases C. increases; moment of inertia decreases D. increases; moment of inertia increases
Answer: C Recall that when we can ignore external torque, Angular Momentum is conserved. In this case, we'll ignore friction in the skate that is touching the ice. In that case, the skater's angular momentum (L) should remain unchanged during this maneuver: Li=LfLi=Lf Recall that angular momentum can be defined as Moment of Inertia (I) times angular velocity (ωω): L=I∗ωL=I∗ω This definition along with conservation of angular momentum gives: Ii∗ωi=If∗ωfIi∗ωi=If∗ωf When the skater pulls her arms and leg toward her center, she is moving more of her mass closer to her axis of rotation, there by decreasing her moment of inertia. Thus her angular velocity increases to conservation her angular momentum.
At the bowling alley, the ball-feeder mechanism must exert a force to push the bowling balls up a 1.0-m long ramp. The ramp leads the balls to a chute 0.5 m above the base of the ramp. Approximately how much force must be exerted on a 5.0-kg bowling ball? A. 200 N B. 50 N C. 25 N D. 5.0 N E. impossible to determine
Answer: C The force exerted by the mechanism times the distance of 1.0 m over which the force is exerted must equal the change in the potential energy of the ball.
For general projectile motion, which of the following best describes the horizontal component of a projectile's velocity? Assume air resistance is negligible. A. The horizontal component of a projectile's velocity is zero. B. The horizontal component of a projectile's velocity continually increases. C. The horizontal component of a projectile's velocity remains a constant. D. The horizontal component of a projectile's velocity continually decreases. E. The horizontal component of a projectile's velocity initially decreases and then increases.
Answer: C The horizontal component of a projectile's velocity remains a constant.
If all three collisions in the figure shown are totally inelastic, which causes the most damage? A. I B. II C. III D. I, II E. I, III F. II, III G. All three
Answer: C The right car in III loses more kinetic energy in the collision than the right car in II or the wall (which has zero kinetic energy) in I. Since any amount of kinetic energy lost goes into deforming the cars, the most damage occurs in III.
Identical constant forces push two objects A (mass m) and B (mass 4m) from rest at a starting line continuously the same distance to a finish line across a frictionless surface. Which object will have a greater kinetic energy at the finish line? A. A B. B C. Both have the same kinetic energy Not enough information to decide
Answer: C The same force pushes both objects the same distance, so both objects have had the same external work done on them. As they both started from rest, by the work-energy theorem they will have the same kinetic energy.
A 1-kg ball is hung at the end of a rod 1-m long. If the system balances at a point on the rod 0.25 m from the end holding the mass, what is the mass of the rod? A. ¼ kg B. ½ kg C. 1 kg D. 2 kg E. 4 kg
Answer: C The total torque about the pivot must be zero! The CM of the rod is at its center, 0.25 m to the right of the pivot. Because this must balance the ball, which is the same distance to the left of the pivot, the masses must be the same
Two identical ping pong balls are selected for a demonstration. A tiny hole is drilled in one of the balls and the ball is filled with water. The hole is sealed so that no water can escape. The two balls are then dropped from rest at the exact same time from the roof of a building. Assuming there is no wind, which of the following statements is true? A. The heavier ball reaches the ground a long time before the lighter ball. B. The heavier ball reaches the ground just before the lighter ball. C. The two balls reach the ground at the same time. D. The heavier ball has a much larger velocity when it strikes the ground than the lighter ball. E. The heavier ball has a slightly larger velocity when it strikes the ground than the lighter ball.
Answer: C The two balls reach the ground at the same time.
A child gets on a shallow playground slide. After pushing himself to get started down the slide he slides at a constant speed all the way to the bottom. Compare the change in gravitational potential energy of the child to the work done on the child by friction. A. Wf is greater than ΔUg B. Wf is less than ΔUg C. Wf is equal to ΔUg
Answer: C Wf is equal to ΔUg
A ball rolls up a hill, stops, then rolls back down the hill. Assume up is the positive direction. At the moment that the ball is stopped, what is its instantaneous acceleration? A. positive B. zero C. negative
Answer: C negative
A cart (weight w1) is attached by a lightweight cable to a bucket (weight w2) as shown. The ramp is frictionless. The pulley is frictionless and does not rotate. When released, the cart accelerates up the ramp and the bucket accelerates downward. How does the cable tension T compare to w2? A. T = w2 B. T > w2 C. w2 > T D. Two of the above are possible, depending on the acceleration. E. All three of the above are possible, depending on the acceleration.
Answer: C w2 > T
An arrow is launched vertically upward. It moves straight up to a maximum height, then falls to the ground. The trajectory of the arrow is noted. Which graph best represents the vertical velocity of the arrow as a function of time? Ignore air resistance; the only force acting is gravity. A.A B. B C. C D. D E. E
Answer: D
Two children sit on opposite ends of a uniform seesaw which pivots in the center. Child A has a mass 60 kg and sits 2.0 m from the center. Child B has a mass 40 kg. How far from the center must child B sit for the seesaw to balance? A. 1.3 m B. 1.5 m C. 2.5 m D. 3.0 m E. can not be determined without the mass of the seesaw
Answer: D
A box sits on a flat board. You lift one end of the board, making an angle with the floor. As you increase the angle, the box will eventually begin to slide down. Why? A. Component of the gravity force parallel to the plane increased B. Coefficient of static friction decreased C. Normal force exerted by the board decreased E. Both a) and c) F. All of a) , b), and c)
Answer: D As the angle increases, the component of weight parallel to the plane increases, and the component perpendicular to the plane decreases (and so does the normal force). Because friction depends on normal force, we see that the friction force gets smaller and the force pulling the box down the plane gets bigger.
The diagram shows two blocks (on a frictionless horizontal surface) with two external forces acting, one on each block as shown. Compared to the net force on the smaller block, the net force on the larger block is _____ A. equal in magnitude & opposite in direction. B. equal in magnitude & in the same direction. C. larger in magnitude & opposite in direction. D. larger in magnitude & in the same direction. F. smaller in magnitude & opposite in direction. G. smaller in magnitude & in the same direction. H. zero, since both net forces vanish & have no direction.
Answer: D The applied forces keep the blocks together & moving to the right with the same acceleration. The net force on each block is equal to its mass times that acceleration, so both net forces are in the same direction (as the acceleration), but the magnitude of the one on the larger block, Fnet = ma, is larger (because its mass is larger).
A cart on an air track is moving at 0.5 m/s when the air is suddenly turned off. The cart comes to rest after traveling 1 m. The experiment is repeated, but now the cart is moving at 1 m/s when the air is turned off. How far does the cart travel before coming to rest? A. 1 m B. 2 m C. 3 m D. 4 m E. 5 m F. impossible to determine
Answer: D The cart comes to a stop when all of the cart's kinetic energy is lost to friction. The frictional force times the stopping distance is equal to the cart's initial kinetic energy.
A car is being pulled slowly by a tow truck. The tension in the tow rope is 400N and a 200N friction force opposes the motion. With these two horizontal forces acting on the car, the car's acceleration is 0.1 m/s2. If the tension in the tow rope is increased to 600N, but the 200N friction force remains constant, what is the car's new acceleration. A.0.05 m/s^2 B. 0.10 m/s^2 C. 0.15 m/s^2 D. 0.20 m/s^2 E. 0.30 m/s^2 F. 0.40 m/s^2 H.0.60 m/s^2 I. 0.80 m/s^2
Answer: D 0.20 m/s^2
A particle moving along the x-axis experiences the net force shown in the graph. The particle starts at rest at xi = 0. What is the kinetic energy of the particle when it reaches xf = 4 m? A. 0.0 J B. 1.0 J C. 2.0 J D. 4.0 J E. 8.0 J
Answer: D 4.0 J
A bobsledder pushes her sled across horizontal snow to get it going, then jumps in. After she jumps in, the sled gradually slows to a halt. What forces act on the sled just after she's jumped in? A. Gravity and kinetic friction B. Gravity and a normal force C. Gravity and the force of the push D. Gravity, a normal force, and kinetic friction E. Gravity, a normal force, kinetic friction, and the force of the push
Answer: D Gravity, a normal force, and kinetic friction
Dr. Morris forgot to turn the air on for the air track. She pushes the cart across the air track to get it going, then lets go. After letting go, the cart quickly slows to a halt. What forces act on the cart just after she lets go? We will ignore air resistance. A. Gravity and kinetic friction B. Gravity and a normal force C. Gravity and the force of the push D. Gravity, a normal force, and kinetic friction E. Gravity, a normal force, kinetic friction, and the force of the push
Answer: D Gravity, a normal force, and kinetic friction
A ball of mass m sits atop a table. The tabletop is a distance d above the ground. The gravitational potential energy for the ball is equal to: A. mgd. B. zero. C. -mgd. D. any value you choose.
Answer: D Only differences in potential energy are relevant, the zero can be chosen to be anywhere.
The figure represents a multiple-flash photo of two balls moving to the right, and shows both balls at several numbered times. In the figure... A. Neither ball passes the other. B. Both balls are accelerating at a non-zero steady rate. C. The upper ball passes the bottom ball. D. The two balls have the same acceleration.
Answer: D The two balls have the same acceleration.
An action/reaction pair of forces A. point in the same direction. B. act on the same object. C. are always long-range forces. D. act on two different objects.
Answer: D act on two different objects.
When do these two objects have the same speed? A.t=0 B. t=1 C. t=2 D. t=3 E. t=4 F. t=5 H. never
Answer: D t=3
A bobsledder pushes her sled across horizontal snow to get it going. The sled starts from rest. After she jumps in, the sled gradually slows to a halt. What forces act on the sled just before she's jumped in? A. Gravity and kinetic friction B. Gravity and a normal force C. Gravity and the force of the push D. Gravity, a normal force, and kinetic friction E. Gravity, a normal force, kinetic friction, and the force of the push
Answer: E Gravity, a normal force, kinetic friction, and the force of the push
A car goes around a curve of radius r at a constant speed v. Then it goes around the same curve at half of the original speed. What is the centripetal acceleration of the car as it goes around the curve for the second time, compared to the first? A. Twice as big B. Four times as big C. The same D. Half as big E. One-fourth as big
Answer: E One-fourth as big
The following two expressions are for kinetic energy (K) and gravitational potential energy (Ug): K=1/2mv2K and Ug=mgy Slingshots are used to shoot two identical pebbles straight up into the air. The first pebble has an initial velocity v (when it leaves the slingshot) and rises to a height H above the slingshot. Pebble two has an initial velocity 4v. How high above the slingshot does this pebble rise? A. H/16 B. H/4 C. H/2 D. 2H F. 4H G. 16H
Answer: F 4H
A box is sliding down a ramp at constant speed. The work done by gravity is _______ compared to the work done by friction A. greater in magnitude and has the same sign B. greater in magnitude and has the opposite sign C. lesser in magnitude and has the same sign D. lesser in magnitude and has the opposite sign E.equal in magnitude and has the same sign F. equal in magnitude and has the opposite sign
Answer: F Since the box's speed is constant, the total net work being done on the box must be zero. This means that the work done by gravity and the work done by friction must sum to zero.
If all three collisions in the figure shown here are totally inelastic, which brings the car on the left to a halt? A. I B. II C. III D. I, II F. I, III G.II, III H. All three
Answer: G Momentum conservation tells us that all three collisions bring the left-hand car to a halt.
For general projectile motion with no air resistance, the horizontal component of a projectile's acceleration A. is always zero. B. remains a non-zero constant. C. continuously increases. D. continuously decreases. E. first decreases and then increases.
Answer:A A. is always zero.
Consider the following free-body diagram for a ball: Which of the following situations could the diagram apply to? Choose all that apply. A. The ball is held at rest in your hand. B. The ball is falling downward after being dropped. C. The ball is moving upward just after being thrown upward.
Answer:A The ball is held at rest in your hand.
A plywood box sits on a frozen pond. At different times you throw a golf ball and a ball of clay (both of the same mass) at the box. The golf ball bounces off the box, while the ball of clay sticks to it. Assuming you throw both balls with the same speed, the change in momentum of the box due to these collisions is A. greater for the golf ball. B. greater for the ball of clay. C. the same for both. D. exactly zero.
Answer:A greater for the golf ball.
A crate is moving to the right on a conveyor belt without slipping. The conveyor belt has been running for a while and maintains a constant speed. The force of friction on the crate is A. to the right B. zero C. to the left
Answer:B The crate is not accelerating, so there is no net force needed to keep it going. It wouldn't slide against the conveyor belt even if it could, so friction does not need to do anything.
The graph shows the potential energy U for a particle that moves along the x-axis. The particle is initially at x = d and moves in the negative x-direction. At which of the labeled x-coordinates does the particle have the greatest speed? A. at x = a B. at x = b C. at x = c D. at x = d
Answer:B at x = b
To get to the second floor of the physics building, student A takes the elevator straight up, while student B walks up the stairway. Assuming that both students have the same mass, which of the following statements is true about the change in their gravitational potential energy after reaching the second floor? A. Student A has greater change in potential energy because he gets to the second floor faster. B. Student B has greater change in potential energy because he has traveled a greater distance. C. Both students have the same change in potential energy. D. It is impossible to tell because potential energy depends on the time elapsed and distance traveled.
Answer:C Both students have the same change in potential energy.
A block slides with no friction along a vertical loop-the-loop, which force becomes zero if block-loop contact is lost? A. The gravitational force on the block (weight) B. The friction force on the block C. The normal force on the block D. The tension force on the block E. The air drag force on the block F. The centripetal force on the block G. None of these
Answer:C The normal force on the block
A uniform disk, a uniform hoop, and a uniform solid sphere are released at the same time at the top of an inclined ramp. They all roll without slipping. In what order do they reach the bottom of the ramp? A. disk, hoop, sphere B. hoop, sphere, disk C. sphere, disk, hoop D. sphere, hoop, disk E. hoop, disk, sphere
Answer:C sphere, disk, hoop
A 1200-kg car moving at 15.6 m/s suddenly collides with a stationary car of mass 1500 kg. If the two vehicles lock together, what is their combined velocity immediately after the collision? A. 5.5 m/s B. 8.6 m/s C. 12.1 m/s D. 6.9 m/s
Answer:D 6.9 m/s
Tuna Hockey: A hockey puck (m = 0.300 kg) sliding at 15 m/s across slippery ice strikes a can of tuna ( m = 0.400 kg) initially at rest and continues on at an angle of 25.0 degrees to its initial line of motion. The dented tuna can moves off at an angle of 40.0 degrees as shown. For the puck-can system, during which portion of the motion does mechanical energy remain constant? A. The entire motion. B. From the start to just before the collision. C. From just after the collision to the end. D. At all times except during the collision. E. None of these.
Answer:D The tuna can is dented after the collision, so mechanical energy has been converted. However, with essentially frictionless ice, there is nothing to change the mechanical energy of the system other than the collision itself.
Ball 1, with the initial velocity shown, collides head on with ball 2, which was initially at rest. If this is a perfectly elastic collision, under what condition will both balls be moving to the right (→) after the collision? A. m2 > m1 B. m1 ≤ m2 C. m1 = m2 D. m1 ≥ m2 E. m1 > m2
Answer:E m1 > m2
Convert 12.030 cm to km (remember to include the correct number of significant figures). There are 100 cm in 1 m and 1000 m in 1 km. A. 0.0001203 B. 0.00012030 C. 0.000001203 D. 0.0000012030 E. 0.00000123
B Convert to the base unit of length first: cm to m (1 cm = 10-2m), and then convert the value in m to km (1 m = 10-3m). Make sure you use the correct conversion factor so that you end up with the units you need.
A monkey is relaxing on a tree branch inclined at an angle θθ with the ground. Which of the Free Body Diagrams below is correct? (Be careful; the relative lengths of the vectors matters!) A. A B. B C. C D. D
Weight must point straight down, so that narrows the choices down to B, C, and D. The normal force must point perpendicularly to the tree branch, so that leaves only B and C. Finally, the frictional force should exactly counteract the x-component of weight . The frictional force on B is too long, so that leaves C.
Report the following sum to the correct number of significant figures: 1.008 g + 126.90 g = _______ A. 127.908 g B. 127.91 g C. 127.90 g D. 127.9 g
When you add, the number to the right of the decimal determines the accuracy of the measurement. All digits to the left are kept. Answer: B
For the following, determine whether: A) energy conservation is useful B) work done is useful C) neither energy nor work are useful Answer Why do air bags reduce injuries from car accidents? If you drop various balls, how high do they bounce? Two athletes collide, how fast do they recoil?
Why do air bags reduce injuries from car accidents? - Work done is useful. If you drop various balls, how high do they bounce? - Energy conservation is useful. Two athletes collide, how fast do they recoil? - Neither energy nor work are useful
