physics exam 2
A frictionless pulley of negligible mass is hung from the ceiling using a rope, also of negligible mass. Two masses, m1 and m2 (m1 < m2) are connected to the rope over the pulley. The masses are free to drop. The magnitude of the tension Ttop is ____ the sum of the weights W1 = m1g and W2 = m2g. (picture with pully)
A) less than
A body of weight w is in free fall near the surface of Earth. What force does the body exert on the Earth?
A) w
What is the force needed to move the mass at a constant speed?
B) 1/2mg
A block is placed on a plane whose angle of inclination is 30º. The coefficients of static and kinetic friction for the block on the inclined plane are both 0.2. The block
B) accelerates down the inclined plane.
A mass m is hanging on a string that passes over a pulley and is then attached to another mass 3m that is resting on a horizontal table. Neglect friction. Mass m is held motionless and is then released. When it has fallen a distance h, it will have a speed v which can be calculated from the formula
B) v=sqrt(gh/2)
The work expended to accelerate a car from 0 to 30 m/s
C) is less than that required to accelerate it from 30 m/s to 60 m/s.
The graph represents the force acting on a body plotted against the displacement of the body in the direction of the force. The total work done by the force from x = 0 to x = x is (graph with slope . line)
E) 1/2·mx^2+ bx
A boy sits in a tire that is attached to a rope that passes over a pulley fastened to the ceiling and then passes back down to the boy's hands. The weight of the boy plus the tire is W. The force with which the boy must pull on the free end of the rope to support his weight in the tire is
A) (1/2)W
A mass 2m is attached by a string to another mass m as illustrated. A force of N newtons acts on mass m to accelerate the system. The force F in the string, which acts on mass 2m, is (box with 2m line with F box with me and line N)
A) (2/3)N
If vector A= -2 i+ 3j and a vector B= 4 i- 5j, the inner product A· B is
A) -23
A car and its occupants, with a total mass m, are moving at a speed v relative to an observer on the side of the road. You are driving in another car, also traveling at speed v, and in the same direction as the first car. The kinetic energy of the first car relative to you is
A) 0
A mass m = 2.5 kg is sliding along a frictionless table with initial speed v as shown in the figure. It strikes a coiled spring that has a force constant k = 500 N/m and compresses it a distance x2 - x1 = -5.0 cm. The initial speed v of the block was (table with spring 2 boxes)
A) 0.71 m/s
A 75-kg man climbs the stairs to the fifth floor of a building, a total height of 16 m. His potential energy has increased by
A) 1.2 × 10^4J
A mass m2 = 1.5 kg rests on a horizontal table. The coefficients of friction between m2 and the table are µs =0.3 and µk = 0.25. The mass m2 is attached by strings to masses m1 = 2.5 kg and m3 = 4.5 kg as shown. Masses m1 and m3 hang freely. The system is initially held at rest. After it is released, the acceleration of m2 is approximately (3 boxes with weights on a table)
A) 1.9 m/s2
You are riding an elevator that is accelerating upward at 2.20 m/s2 You have a spring balance accurately calibrated in newtons. When you hang a mass of 10.0 kg on the balance, the reading of the balance is
A) 120 N
A particle moving with uniform Motion Along a Curved Path has a period of 0.24 s and a speed of 4.2 m/s. The radius of the path of the particle is
A) 16 cm
The object in the figure has a mass of 3.45 kg and is pulled up a slope AB, which is 36 m long; the height BC is 3.00 m. There is no friction and the acceleration is constant. The speed v1 at A is 3.5 m/s whereas the speed v2 at B is 5.5 m/s. The average power developed by the motor pulling the object is (big triangle with a b c)
A) 17 W
A block with a mass M = 4.85 kg is resting on a slide that has a curved surface. There is no friction. The speed of the block after it has slid along the slide sufficiently far for its vertical drop to be 19.6 m is
A) 19.6 m/s
An object with a mass M = 250 g is on a plane inclined at 30º above the horizontal and is attached by a string to a mass m = 150 g. There is no friction and mass m hangs freely and is initially at rest. When mass m has descended a distance h = 10 cm, its speed will be
A) 35.0 cm/s
Three blocks are connected by massless cords and hung by a third massless cord to a beam. Mass m1 = 2 m2 = 3 m3. Mass m1 is the lowest block and m3 is the highest. The tension in the cord between the two highest blocks is
A) 3m1 × g/2
A bullet with a mass of 12 g moving horizontally strikes a fixed block of wood and penetrates a distance of 5.2 cm. The speed of the bullet just before the collision is 640 m/s. The average force that the wood exerted on the bullet was
A) 4.7 × 104N
Three blocks are connected by massless cords and rest on a frictionless horizontal surface. The blocks are pulled to the right. Mass m1 = 2 m2 = 3 m3, with m1 on the left and m3 on the right. If the pulling force is equal to 90 N, then the tension in the cord between m1 and m2 is (m1 box m2 box m3box line F)
A) 49 N
The angle between the vector A= i+ 2j + 3ˆk and the y axis is approximately
A) 58º
A vertical rope is attached to an object that has a mass of 40.0 kg and is at rest. The tension in the rope needed to give the object an upward speed of 3.50 m/s in 0.700 s is
A) 592 N
An object with a mass M = 250 g is at rest on a plane that makes an angle θ = 30º above the horizontal. The coefficient of kinetic friction between M and the plane is µk = 0.100. Mass M is attached by a string to another mass, m = 200 g, which hangs freely. When mass m has fallen 30.0 cm, its speed is (triangle two weights on a pully)
A) 83 cm/s
A woman runs up a flight of stairs. The gain in her gravitational potential energy is U. If she runs up the same stairs with twice the speed, what is her gain in potential energy?
A) U
The potential energy function for a conservative force acting in the x direction is shown in the figure on the right. Where would the particle experience a force directed to the right? (graph with sqiggle line and letters)
A) between A & B and E & F
A 5-kg object slides down a frictionless surface inclined at an angle of 30º from the horizontal. The total distance moved by the object along the plane is 10 meters. The work done on the object by the normal force of the surface is
A) zero
A particle moves halfway around a circle of radius R. It is acted on by a radial force of magnitude F. The work done by the radial force is
A) zero
A car going around a curve of radius R at a speed V experiences a centripetal acceleration ac. What is its acceleration if it goes around a curve of radius 3R at a speed of 2V?
B) (4/3)ac
Two masses m1 and m2 (with m2 > m1) are connected by a massless rope hung over a frictionless light pulley. If the masses are released then the acceleration of m2 in the downward direction is given by (picture of a pully)
B) (m2 − m1) × g/(m1 + m2)
A 10-kg box is pushed up a plane inclined at 37º with the horizontal. The box starts from rest and is pushed 5 m along the incline with a uniform acceleration of 2 m/s2. The coefficient of kinetic friction is 0.20 and the pushing force is parallel to the plane. The increase in the potential energy of the box is
B) 0.29 kJ
A 6.0-kg block slides from point A down a frictionless curve to point B. After the block passes point B, a friction force opposes the motion of the block so that it comes to a stop 2.5 m from B. Calculate the coefficient of kinetic friction between the block and the surface after position B. (a b slope parabal thing going down)
B) 0.40
For this problem, assume no friction. A mass m2 = 3.5 kg rests on a horizontal table and is attached by strings to masses m1 = 1.5 kg and m3 = 2.5 kg as shown. The masses m1 and m3 hang freely. The system is initially held at rest. After it is released, the acceleration of mass m2 will be (table with mass on the table and cord with masses on both ends)
B) 1.3 m/s2
Kids love to crash their toy cars together. One such collision involves a 0.5 kg car moving at 0.3 m/s colliding with a stationary toy car of mass 0.3 kg. The two toys stick together and move away from the collision point at 0.188 m/s. By what factor is the initial kinetic energy greater than the final kinetic energy?
B) 1.6
A horse-drawn coach is decelerating at 3.0 m/s2 while moving in a straight line horizontally. A 350-g mass is hanging on a string 1.6 m long from the ceiling of the coach. The angle that the string makes with the vertical is
B) 17º toward the front of the coach.
A 4.0-kg block starts from rest and slides 5.0 m down a plane inclined at 60º to the horizontal. The coefficient of kinetic friction between the surface and the block is 0.20. The work done by friction on the block is
B) 19.6 J
When the potential energy U(r) is given as in Figure A, then the force is given in Figure B by curve (2 graph with straight line graph with 3 straight lines and 2 random ones)
B) 2
A mass M = 5.6 kg on a horizontal table is pulled by a horizontal string that passes over a frictionless pulley to a free-hanging mass m = 3.4 kg. The coefficient of friction between M and the table is 0.28. The acceleration of M is
B) 2.0 m/s2
In magazine car tests an important indicator of performance is the zero to 60 mph (0 to 96.6 km/h) acceleration time. A time below 6 s is considered to be extremely quick. If a car with mass 1300 kg were dropped vertically from a great height, how long would it take to go from zero to 60 mph and what would the magnitude of the change in gravitational potential energy be during this time? (neglect air resistance)
B) 2.74 s and 468 kJ
A block with a mass of 10 kg is at rest on a horizontal surface. The coefficient of static friction between the block and the surface is 0.30, and the coefficient of kinetic friction is 0.25. A force of 20 N acts on the block toward the left. The magnitude of the frictional force on the block is
B) 20 N
A 44.5-N weight is hung on a spring scale, and the scale is hung on a string. The string is lowered at a rate such that the entire assembly has a downward acceleration of 4.90 m/s2 . The scale reads
B) 22.2 N
What minimum power rating must a water pump have if needs to raise water at 20 kg per minute from a depth of 9 m?
B) 29.4 W
Three forces F1, F2 and F3 act on an object. If F1 = 3Ni+ 5N j + 7N k, F2 = −5N i − 2Nj −2N k, and the object is moving at constant velocity then the vector force F3 is
B) 2N i − 3N j − 5N k
Two objects are sliding at the same speed across a wooden surface. The coefficient of kinetic friction between the first object and the surface is twice that between the second object and the surface. The distance traveled by the first object before it stops is S. The distance traveled by the second object is
B) 2S
A mass m is traveling at an initial speed v0 = 25.0 m/s. It is brought to rest in a distance of 62.5 m by a force of 15.0 N. The mass is
B) 3.00 kg
A Blackhawk helicopter is winching up an injured soldier from a danger zone. The soldier and his kit have a mass of 150 kg and are pulled up 50 m in the air at a steady rate. If it takes 30 s to pull the soldier up, how much power has been used by the helicopter's 65% efficient winch engine?
B) 3.8 kW
An astronaut lands on an Earthlike planet and drops a small lead ball with a mass of 76.5 g from the top of her spaceship. The point of release is 18 m above the surface of the planet and the ball takes 2.5 s to reach the ground. The astronaut's mass on Earth is 68.5 kg. Her weight on the planet is
B) 395 N
A 6.0-kg block slides from rest at position A down a frictionless incline to position B. The speed of the block at B is (a b slope parabal thing going down with box at the top)
B) 4.4 m/s
Three smiley faces are situated along the x axis as follows: m1 = 5 kg at 3.0 m, m2 = 3 kg at 6.0 m and m3 = 2 kg at 8.0 m. Where is the center of mass situated? (3 smile faces on line)
B) 4.9 m
You want to elope by sliding down a nylon rope made by tying stockings together. The rope will withstand a maximum tension of 300 N without breaking. Your mass is 61.2 kg. The magnitude of the smallest acceleration a with which you can slide down the rope is
B) 4.91 m/s2
A system comprising two blocks is shown, one of which is on an inclined plane. The pulley is of negligible mass and is frictionless. The system starts from rest at position 1 and accelerates. Measurements taken when the blocks reach position 2 indicate that (1) the kinetic energy of block A has changed by 330 J; (2) the potential energy of block A has changed by 588 J; (3) the kinetic energy of block B has changed by 110 J; and (4) the potential energy of block B has changed by 98 J. The amount of mechanical energy that has been converted to heat because of friction is
B) 50 J
An object with a mass of m = 12.0 g is falling through a resistive fluid in which g is constant. The retarding frictional force due to the fluid is F = bv, where F is the force in newtons, b is a constant, and v is the speed in meters per second. If F = 3.2 × 10-2 N when v = 16.0 m/s, the terminal speed of the object falling through the fluid is
B) 59 m/s
The block shown in the figure is sliding on a frictionless surface. Its speed when it reaches the level portion of the surface on which it is sliding will be ( pic ramp that says frictionles surface)
B) 7.67 m/s
A horse exerts a force F on a cart, causing the cart to move with increasing speed. What force does the cart exert on the horse?
B) F
According to Quantum Chromodynamics, the force that keeps quarks confined within a proton (or neutron) increases as the separation between the individual quarks increases. Which statement below best represents this scenario?
B) The quarks are tied together by elastic strings.
A body falls through the atmosphere (consider air resistance) gaining 20 J of kinetic energy. How much gravitational potential energy did it lose?
B) more than 20 J
A horizontal force F acts on a mass m that lies on a horizontal surface. The acceleration of m is a(arrow) The coefficient of kinetic friction µk between mass m and the surface can be calculated from
B) µk = (F/mg) - (a/g)
A 10-kg box is at the top of a 5-m plane inclined at 37º with the horizontal. The box starts from rest and slides down the plane. The coefficient of kinetic friction is 0.20. The magnitude of the change in the potential energy of the box is
C) 0.29 kJ
A mass of 25 kg is acted on by two forces: F1 is 15 N due east, and F 2 is 10 N due north. The acceleration of the mass is
C) 0.72 m/s2 ,33.7º north of east.
What is the work done by a car's braking system when it slows the 1500-kg car from an initial speed of 96 km/h down to 56 km/h in a distance of 55 m?
C) 1.3 MJ
The kinetic energy of a car is 1.00 × 105 J. If the car's speed is increased by 20 percent, the kinetic energy of the car becomes
C) 1.44 × 105J
You ride a roller coaster car of mass 1500 kg down a frictionless track a distance H = 23m above the bottom of a loop as shown. If the loop is 15 m in diameter, the downward force of the rails on your car when it is upside down at the top of the loop is (pic of rollercoaster)
C) 1.7 × 10^4N
If the force is applied over a distance, d, the distance the mass moves is (2 curvy pullys)
C) 1/2d
A 5-kg box is pushed 5 m up a plane that is inclined at 30º with the horizontal. The coefficient of kinetic friction between the box and the plane is 0.20. The change in potential energy of the box is approximately
C) 123 J
The angle between the vectors A = -2 i+ 3j and B= 4 i- 5j is approximately
C) 175º
A 5-kg object undergoes a displacement ∆ s= 2 i+ 3j. During the displacement, aconstant force F= 4 i- 2j acts on the object. All values are given in SI units. The work done by the force F on this object is
C) 2 J
A motor is lifting a mass of 35.0 kg at a constant speed of 6.00 m/s. If friction is neglected, the power developed by the motor to do this lifting is
C) 2.1 × 10^3W
Two forces, both of magnitude 12 N and directed 35 degrees either side of the direction of motion, pull a crate 15 m. How much work is done by the forces in moving the crate?
C) 2.9 × 10^2J
Release mass m on a string from rest at point A. As it passes the lowest point B, the tension in the string is (graph with A B R R/2)
C) 2mg
Section: 7-1 Topic: Potential Energy Type: Conceptual 148 Which potential energy versus displacement curve best represents that of an extended spring? (5 diff graphs)
C) 3
A professor likes to demonstrate centripetal force by swinging a bucket of water in the vertical direction. What is the minimum speed he must swing the bucket at the top of the circle if he is not to get drenched? (Assume that his arm is 1 m long.)
C) 3.1 m/s
In a television tube, an electron starting from rest experiences a force of 4.0 × 10−15 N over a distance of 50 cm. The final speed of the electron is (do not worry about relativistic effects):
C) 3.3 × 10^7m/s
A 5200-kg cable car in Hong Kong is pulled a distance of 360 m up a hill inclined at 12º from the horizontal. The change in the potential energy of the car is
C) 3.8 × 10^6J
Egyptian pyramid workers push a 1200-kg block up an incline that has an angle of 69 degrees to the vertical, at a constant speed of 0.5 m/s. The coefficient of kinetic friction between the block and the incline surface is 0.44. How much power must the workers supply?
C) 4.5 kW
A tired worker pushes a heavy (100-kg) crate that is resting on a thick pile carpet. The coefficients of static and kinetic friction are 0.6 and 0.4, respectively. The worker pushes with a force of 500 N. The frictional force exerted by the surface is
C) 500 N
A 50-kg box is placed in the bed of a truck. The coefficient of friction between the box and the truck bed is 0.54. If the truck is traveling at 87 km/h (~54 mph) then calculate the minimum distance the truck can stop in without the box sliding into the cab.
C) 55 m
Four smiley faces are situated along the x axis as follows: m1 = 5 kg at 0.0 m, m2 = 3 kg at 4.0 m, m3 = 3 kg at x m, and m4 = 2 kg at 8.0 m. If the center of mass is situated at 3.54 m, where is m3 located? (4 smile faces)
C) 6.0 m
The acceleration due to gravity on the moon is only about 1/6 of that on Earth. An astronaut whose weight on Earth is 600 N travels to the lunar surface. His mass as measured on the moon is
C) 61.2 kg
A donkey is attached by a rope to a wooden cart at an angle of 23° to the horizontal. The tension in the rope is 210 N. If the cart is dragged horizontally along the floor with a constant speed of 6 km/h, calculate how much work the donkey does in 35 minutes.
C) 680 kJ
A woman on a bicycle traveling at 10 m/s on a horizontal road stops pedaling as she starts up a hill inclined at 3.0º to the horizontal. If friction forces are ignored, how far up the hill does she travel before stopping?
C) 97 m
The potential energy function for a conservative force acting in the x direction on a particle is shown below. The number of points where the net force on the particle is equal to zero are (graph with sqiggle line and letters)
C) B, C, D, and E.
A heavy truck and a light car are traveling at the same speed on the same roadway. If the coefficients of static friction between their tires and the road are the same, which vehicle will be able to stop in the shortest distance? Assume both have the same braking force.
C) Both will be able to stop in the same distance.
Three boxes are connected by stretchless strings and are pulled by a force F as shown in the figure. Which string has to be the strongest so as not to break? (3 boxes 1,2,3 and line conected at end with F
C) C
Susana ascends a mountain via a short, steep trail. Sean ascends the same mountain via a long, gentle trail. Which of the following statements is true?
C) Susana gains the same gravitational potential energy as Sean.
A 50-kg block rests on a horizontal surface. The coefficient of static friction µa = 0.50. The coefficient of kinetic friction µk = 0.35. A force P of 250 N is applied as shown. (picture with box line F)
C) The block accelerates to the right.
The work done by a conservative force between two points is
C) always independent of the path.
Three forces, X,Y, and Z , act on a mass of 4.2 kg. The forces are X= 2.0 N acting to the east, Y= 5.0 N acting 45º to the north of east, and Z= 4.0 N acting 30º to the north of west. The direction of the net acceleration
C) is 70º north of east.
A horizontal force F is used to push an object of mass m up an inclined plane. The angle between the plane and the horizontal is θ. The normal reaction force of the plane acting on the mass m is
C) mg cos θ + F sinθ
A mass, m, slides down a frictionless incline and hits a spring with spring constant k. Find the spring compression when the acceleration of the mass is zero. (triangle with spring)
C) mg sin θ/k
A ball of mass 2.0 kg is acted on by two forces, F1=3.0Ni+4.0Nj and F2=-5Ni+6Nj At t = 0 s, the particle is at rest at the origin. The velocity vector at t = 2 s is
C) r=-2.0m/si+10.0m/sj
Assuming the incline to be frictionless and the zero of gravitational potential energy to be at the elevation of the horizontal line, (triangle with spring)
C) the kinetic energy of the block when it has fully compressed the spring will be zero.
A roller coaster starts from rest at point A. If you ignore friction and take the zero of potential energy to be at C, (rollercoaster pic)
C) the kinetic energy of the coaster at C will be equal to its potential energy at A.
The total mechanical energy of any system is
C) the sum of the kinetic and potential energy at any point.
A block of mass m starts from position 1 and moves up a frictionless inclined plane with an initial speed v. At some later time the block has moved down the plane and at position 2 has a speed u. If a and b are the heights above the bottom of the plane, the magnitude of u can be determined from (triangle with 2 boxes)
C) u^2 = v^2+ 2g(a - b)
Your heart pumps 80 g of blood with each beat. The blood starts from rest and reaches a speed of 0.60 m/s in the aorta. If each beat takes 0.16 s, the average force exerted on the blood is
D) 0.30 N
A 100-kg block is pushed up a 30º incline that is 10 m long. If the coefficient of friction between the block and the incline is 0.1, the constant force parallel to the incline that is required to move the block from rest at the bottom of the incline to the top in 3 s is approximately
D) 0.80 kN
The surface shown in the figure is frictionless. If the block is released from rest, it will compress the spring at the foot of the incline(triangle with spring and 4m k=100N/m)
D) 0.989 m
N from one end of a room to another a distance of 4 m. Given that the vertical component of the pulling force is 12 N, calculate the work done by the force in moving the crate.
D) 1.7 × 10^2J
A 2-kg block sits on an incline where the top part of the incline has a coefficient of kinetic friction (µk) of 0.70. The bottom section of the plane has µk = 0.95. The angle of inclination is 40 degrees. The block is released and travels 10 m along the initial part of the incline and then enters the lower section. Calculate how far the block travels along the second section before it is brought to a stop. (triangle with box at top)
D) 13 m
A body is acted upon by a force of 10 N and undergoes a displacement in the direction of the force in accordance with the relation s = 3t 2+ 2t, where s is the displacement in meters and t is in seconds. The rate at which the force is doing work at the instant t = 2s is
D) 140 W
A body is acted upon by a force of 10 N and undergoes displacement in the direction of the force in accordance with the relation s = 3t^2+ 2t where the units are SI. The rate at which the force is doing work at the instant t = 2 s is
D) 140 W
If a force F is required to extend a spring a distance 5y, how far will it be extended by force 3F?
D) 15y
The power developed by a certain engine is a function of time according to P = 2 + 2t + 3t^2 where the units are SI. The work done by the engine in the interval from t = 0 to t = 2 s is
D) 16 J
An object with a mass of 5.5 kg is allowed to slide from rest down an inclined plane. The plane makes an angle of 30º with the horizontal and is 72 m long. The coefficient of friction between the plane and the object is 0.35. The speed of the object at the bottom of the plane is
D) 17 m/s
A projectile of mass m is propelled from ground level with kinetic energy of 450 J. At the exact top of its trajectory, its kinetic energy is 250 J. To what height above the starting point does the projectile rise?
D) 200/mg m
A particle with a mass of 200 g is acted on by a force of 4.5 N. The acceleration of the particle is
D) 23 m/s2
The graph shows a plot of the gravitational potential energy U of a 1-kg body as a function of its height h above the surface of a planet. The acceleration due to gravity at the surface of the planet is (grid with line)
D) 3.0 m/s2
A 5-kg mass with initial velocity 20 m/s slides along a frictionless horizontal surface then up a frictionless ramp (2 m long and at an angle 30 degrees to the horizontal) and onto a second horizontal surface. The block slides over a rough surface 15 m in length (µk = 0.4) before moving again on a frictionless surface and then impacting upon an uncompressed spring. If the block compresses the spring a distance 2 m, what is the spring constant k for the spring?
D) 32.8 N/m
Rachel has been reading her physics book. She takes her weighing scales into an elevator and stands on them. If her normal weight is 690 N (155 lbs), and the elevator moves upward at 0.25g and then down at 0.25g, what is the difference between the up and down scale readings?
D) 345 N
What is the difference in work needed to push a 100 kg crate (at constant speed) a distance of 2 m along an inclined plane that is at an angle of 20 degrees with the horizontal, if the coefficient of kinetic friction was equal to 0.20 or zero?
D) 370 N
A ball of mass 2.0 kg is acted on by two forces, F1=3Ni+4Nj and F2=-5Ni+6Nj The magnitude of the acceleration is
D) 5.1 m/s2
A particle is moving uniformly in a circle with radius 50 cm. The linear speed of the particle is 60 cm/s. The acceleration of the particle has a magnitude of
D) 72 cm/s2
As a punishment for being late to a practice session the coach orders her star athlete to run up the stadium steps. The player's mass is 80 kg and it takes one minute for her to run up the 120 steps at a constant rate. If each step is of height 0.5 m, what is the power output of the player?
D) 785 W
Initially a body moves in one direction and has kinetic energy K. Then it moves in the opposite direction with three times its initial speed. What is the kinetic energy now?
D) 9K
Which of the following statements is true? A) Friction is a conservative force and does negative work. B) Potential energy may be defined by the equation U(x) = -dF(x)/dx C) The work done by a conservative force between two points depends on the path taken between those points. D) A conservative force cannot change a body's total energy. E) The work done by a conservative force while a body moves at constant velocity must be zero.
D) A conservative force cannot change a body's total energy.
Which of the following statements is true?
D) Potential energy can be negative but kinetic energy cannot.
A ball of mass 2.0 kg is acted on by two forces, F1=3Ni+4Nj and F2=-5Ni+6Nj The acceleration vector of the mass is (in m/s)
D) a=-1.0i+5.0j
Two masses, m1 and m2, connected by a massless string, are accelerated uniformly on a frictionless surface as shown. The ratio of the tensions T1/T2 is given by (box with m1 line t1 box m2 line t2)
D) m1/(m1 + m2)
A 15-kg block sitting on a smooth table is connected to a free-hanging 5-kg mass by a stretchless, massless cord that passes over a small frictionless pulley. The acceleration of the two-block system is
D) one-fourth of g.
Negative work means
D) the applied force is opposite to the displacement.
A ball of mass 2.0 kg is acted on by two forces, F1=3.0Ni+4.0Nj and F2=-5Ni+6Nj At t = 0 s, the particle is at rest at the origin. The position vector at t = 2 s is
D)r=-2.0mi+10.0mj
A spring with force constant k = 300 N/m is compressed 9.0 cm. What is the potential energy in the spring?
E) 1.2 J
Two masses m1 = 12 kg and m2 = 35 kg are held connected by a massless rope hung over a frictionless light pulley. If the masses are released then the magnitude of the tension in the string is
E) 175 N
We all know it makes sense to bend one's knees when dropping from a height. Suppose a very silly 70-kg person were instead to drop down from a height of 1.4 m onto the ground and stop stiffly within a distance of only 0.60 cm. Calculate how many times his own weight is the average force his body feels.
E) 2.3 × 102
A block of wood is pulled by a horizontal string across a rough surface at a constant velocity with a force of 20 N. The coefficient of kinetic friction between the surfaces is 0.3. The force of friction is
E) 20 N
A lamp with a mass m is suspended from the ceiling by two cords as shown. The ratio of the magnitude of the vertical component of the tension in T2 to that in T3 is
E) 3:1
If the average power output of a car engine is the same as a 100-W light bulb, how long would it take a 1200-kg car to go from zero to 96 km/h (60 mph)?
E) 4.3 × 10^3s
A particle of mass 1.3 kg is sliding down a frictionless slope inclined at 30º to the horizontal. The acceleration of the particle down the slope is
E) 4.9 m/s2
The average marathon runner can complete the 42.2-km distance of the marathon in 3 h and 30 min. If the runner's mass is 75 kg, what is the runner's average kinetic energy during the run?
E) 421 J
Car drag racing takes place over a distance of a 1 4 mile (402 m) from a standing start. If a car (mass 1500 kg) could be propelled forward with a pulling force equal to that of gravity, what would be the change in kinetic energy and the terminal speed of the car (in mph) at the end of the race be? (For comparison, a modern, high-performance sports car may reach a terminal speed of just over 100 mph = 44.7 m/s.)
E) 5.92 MJ and 88.9 m/s
A block of mass, m, is pushed up against a spring, compressing it a distance x, and is then released. The spring projects the block along a frictionless horizontal surface, giving the block a speed v. The same spring projects a second block of mass 4m, giving it a speed 3v. What distance was the spring compressed in the second case?
E) 6x
A proud new Jaguar owner drives her car at a speed of 25 m/s into a corner. The coefficients of friction between the road and the tires are 0.70 (static) and 0.40 (kinetic). What is the minimum radius of curvature for the corner in order for the car not to skid?
E) 91 m
A 5-kg blob of putty is dropped from a height of 10.0 m above the ground onto a light vertical spring the top of which is 5 m above the ground. If the spring constant k = 200 N/m and the blob compresses the spring by 1.50 m, then find the amount of energy lost in sound and thermal energy.
E) 94.0 J
A simple pendulum has a bob of mass M. The bob is on a light string of length l. The string is fixed at C. At position A, the string is horizontal and the bob is at rest. The bob is released from A and swings to B, where the string is vertical. The tension in the string when the bob first reaches B is (Little graph with A B C)
E) None of these is correct.
A body moves with decreasing speed. Which of the following statements is true?
E) The net work done on the body is negative, and the kinetic energy is decreasing.
The reference point for gravitational potential energy
E) can be chosen arbitrarily.
The net force acting on an object is zero. You can therefore definitely conclude that the object is
E) either at rest or moving in a straight line at constant speed.
As a sky diver falls through the air, her terminal speed
E) is described by all of the above.
A force F pushes a block along a horizontal surface against a force of friction Ff. If the block undergoes a displacement s at constant velocity, the work done by the resultant force on the block
E) is zero.
A block of mass m is pulled in the direction shown in the figure across a rough surface at a constant velocity. The magnitude of the frictional force is (pic with box and line and angle)
E) µk(mg - T sin θ)