Physics Ch 7
An ideal spring is hung vertically from the ceiling. When a 2.0-kg block hangs at rest from it the spring is extended 6.0 cm from its relaxed length. A upward external force is then applied to the block to move it upward a distance of 16 cm. While the block is moving upward the work done by the spring is:
-1.0J
At time t = 0 a 2-kg particle has a velocity of (4m/s)ˆi − (3m/s)ˆj. At t = 3 s its velocity is (2m/s)ˆi + (3m/s)ˆj. During this time the work done on it was:
-12J
An ideal spring is hung vertically from the ceiling. When a 2.0-kg mass hangs at rest from it the spring is extended 6.0 cm from its relaxed length. A downward external force is now applied to the mass to extend the spring an additional 10 cm. While the spring is being extended by the force, the work done by the spring is:
-3.6J
A block is attached to the end of an ideal spring and moved from coordinate xi to coordinate xf . The relaxed position is at x = 0. The work done by spring is positive if X1=, X2=
-4cm,-2cm
A boy holds a 40N weight at arms length for 10s. His arm is 1.5 m above the ground. The work done by the force of the boy on the weight while he is holding it is
0
A man wishes to pull a crate 15m across a rough floor by exerting a force of 100 N. The coefficient of kinetic friction is 0.25. For the man to do the least work, the angle between the force and the horizontal should be:
0
An object of mass 1g is whirled in a horizontal circle with radius .5m at a constant speed of 2m/s. The work done on the object during one revolution is
0
An escalator is used to move 20 people (60 kg each) per minute from the first floor of a department store to the second floor, 5m above. Neglecting friction, the power required is approximately:
1000W
A 1kg block is lifted vertically 1 m by a boy. The work done by the boy is about
10J
A man pushes an 80-N crate a distance of 5.0m upward along a frictionless slope that makes an angle of 30◦ with the horizontal. His force is parallel to the slope. If the speed of the crate decreases at a rate of 1.5m/s2, then the work done by the man is:
140J
. A 0.50-kg object moves on a horizontal circular track with a radius of 2.5m. An external force of 3.0N, always tangent to the track, causes the object to speed up as it goes around. If it starts from rest its speed at the end of one revolution is:
14m/s
A 5.0-kg cart is moving horizontally at 6.0m/s. In order to change its speed to 10.0m/s, the net work done on the cart must be:
160J
A 4-kg cart starts up an incline with a speed of 3m/s and comes to rest 2m up the incline. The total work done on the car is:
18J
The weight of an object on the moon is one-sixth of its weight on Earth. The ratio of the kinetic energy of a body on Earth moving with speed V to that of the same body moving with speed V on the moon is:
1:1
Two objects with masses of m1 and m2 have the same kinetic energy and are both moving to the right. The same constant force F is applied to the left to both masses. If m1 = 4m2, the ratio of the stopping distance of m1 to that of m2 is:
1:1
A sledge (including load) weights 5000N. It is pulled on level snow by a dog team exerting a horizontal force on it. The coefficient of kinetic friction between sledge and snow is 0.05. How much work is done by the dog team pulling the sledge 1000m at constant speed
2.5*10^5 J
A man pushes an 80-N crate a distance of 5.0m upward along a frictionless slope that makes an angle of 30◦ with the horizontal. The force he exerts is parallel to the slope. If the speed of the crate is constant, then the work done by the man is
200J
An 80-N crate slides with constant speed a distance of 5.0m downward along a rough slope that makes an angle of 30◦ with the horizontal. The work done by the force of gravity is:
200J
A 2 kg object is moving at 3m/s. A 4N force is applied in the direction of motion and then removed after the object has traveled an additional 5m. The work done by this force is
20J
A particle moves 5m in the positive x direction while being acted upon by a constant force F = (4N)ˆi + (2 N)ˆj − (4 N)ˆk . The work done on the particle by this force is:
20J
A 50-N force is the only force on a 2-kg object that starts from rest. When the force has been acting for 2 s the rate at which it is doing work is:
2500 W
The velocity of a particle moving along the x axis changes from vi to vf . For which values of vi and vf is the total work done on the particle positive? Vi=, vf=
2m/s, -5m/s
A 1.5-kg crate falls from a height of 2.0m onto an industrial spring scale with a spring constant of 1.5 × 105 N/m. At its greatest compression the reading on the scale is:
3*10^3N
Camping equipment weighing 6000N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. The work done by the campers in pulling the equipment 1000 m at constant velocity is
3*10^5 J
A crate moves 10 meters to the right on a horizontal surface as a woman pulls on it with 10 N of force. Rank the situation by force least to greatest
3,2,1
A 0.50-kg object moves on a horizontal frictionless circular track with a radius of 2.5m. An external force of 3.0N, always tangent to the track, causes the object to speed up as it goes around. If it starts from rest, then at the end of one revolution the radial component of the force of the track on it is:
38N
Camping equipment weighing 6000N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. How much work is done by the campers in pulling the equipment 1000m if its speed is increasing at the constant rate of 0.20m/s2?
4.2*10^5 J
A 0.50-kg object moves in a horizontal circular track with a radius of 2.5m. An external force of 3.0N, always tangent to the track causes the object to speed up as it goes around. The work done by the external force as the mass makes one revolution is:
47J
Two trailers, X with mass 500 kg and Y with mass 2000 kg, are being pulled at the same speed. The ratio of the kinetic energy of Y to that of X is:
4:1
A man moves the 10-g object shown in a vertical plane from position X to position Y along a circular track of radius 20 m. The process takes 0.75 min. The work done by the man is about:
4J
An object is constrained by a cord to move in a circular path of radius 0.5m on a horizontal frictionless surface. The cord will break if its tension exceeds 16 N. The maximum kinetic energy the object can have is:
4J
A 8000-N car is traveling at 12m/s along a horizontal road when the brakes are applied. The car skids to a stop in 4.0 s. How much kinetic energy does the car lose in this time?
5.9*10^4J
A 50-N force is the only force a 2-kg crate that starts from rest. At the instant the object has gone 2m the rate at which the force is doing work is:
500 W
A man pulls a 100-N crate up a frictionless 30◦ slope 5m high, as shown. Assuming that the crate moves at constant speed, the work done by the man is:
500J
An ideal spring, with a pointer attached to its end, hangs next to a scale. With a 100-N weight attached, the pointer indicates "40" on the scale as shown. Using a 200-N weight instead results in "60" on the scale. Using an unknown weight X instead results in "30" on the scale. The weight of X is:
50N
A 2-kg block is attached to a horizonal ideal spring with a spring constant of 200N/m. When the spring has its equilibrium length the block is given a speed of 5m/s. What is the maximum elongation of the spring?
5m
Three identical ideal springs (X,Y,Z) are arranged as shown. When a 4.0-kg mass is hung on X, the mass descends 3.0 cm. When a 6.0-kg mass is hung on Y, the mass descends:
9.0cm
When a certain rubber band is stretched a distance x, it exerts a restoring force of magnitude F = Ax, where A is a constant. The work done by a person in stretching this rubber band from x = 0 to x = L, beginning and ending at rest, is:
AL2/2
When a certain rubber band is stretched a distance x, it exerts a restoring force of magnitude F = ax+bx2, where a and b are constants. The work done in stretching this rubber band from x = 0 to x = L is:
AL2/2 +AL3/3
A crate is initially at rest on a horizontal frictionless table. A constant horizontal force F is applied. Which of the following five graphs is a correct plot of work W as a function of the crate's speed v?
D
A man pulls a sled along a rough horizontal surface by applying a constant force F at an angle θ above the horizontal. In pulling the sled a horizontal distance d, the work done by the man is:
Fdcostheta
A particle moving along the x axis is acted upon by a single force F = F0e−kx, where F0 and k are constants. The particle is released from rest at x = 0. It will attain a maximum kinetic energy of:
Fnot/k
In raising an object to a given height by means of an inclined plane, as compared with raising
Force required
An 8-N block slides down an incline. It has an initial speed of 7m/s. The work done by the resultant force on this block is:
Impossible to calculate
Which of the following is the correct combination of dimensions for energy?
ML2/T2
Power has the dimensions of
ML2/T3
Which of the following bodies has the largest kinetic energy
Mass 2M and Speed V3
The amount of work required to stop a moving object is equal to
The Kinetic E of the object
An object moves in a circle at constant speed. The work done by the centripetal force is 0 because
The centripetal force is perpendicular to the velocity
The mechanical advantage of any machine is
The ratio of the force exerted by the machine to the force applied to it
A woman lifts a barbell 2.0m in 5.0 s. If she lifts it the same distance in 10 s, the work done by her is:
The same
Which of the following five units represents a quantity that is NOT the same as the other four?
Watt
Which of the following groups does not contain a scalar quantity
displacement, acceleration, force
A watt*second is a unit of
energy
A watt is
kg*m2/s3
Which of the following five quantities is NOT an expression for energy? Here m is a mass, g is the acceleration due to gravity, h and d are distances, F is a force, v is a speed, a is an acceleration, P is power, and t is time.
ma
A Boston Red Sox baseball player catches a ball of mass m that is moving toward him with speed v. While bringing the ball to rest, his hand moves back a distance d. Assuming constant deceleration, the horizontal force exerted on the ball by his hand is:
mv2/2d
A baseball is hit high into the upper bleachers of the left field. Over it's entire flight the work done by gravity and the work done by air resistance , respectively, are
negative, negative
A person holds an 80-N weight 2m above the floor for 30 seconds. The power required to do this is:
none of these
A watt per hour is a unit of
none of these
The work done by gravity during the descent of a projectile is
positive
At time t = 0 a particle starts moving along the x axis. If its kinetic energy increases uniformly with t the net force acting on it must be:
proportional to 1/root(t)
A particle starts from rest and is acted on by a net force that does work at a rate that is proportional to the time t. The speed of the particle is proportional to:
root(t)
. A particle starts from rest at time t = 0 and moves along the x axis. If the net force on it is proportional to t, its kinetic energy is proportional to:
t4
Which of the following is not a correct unit for work
watt
A kilowatt*hour is a unit of
work
A line drive to the shortstop is caught at the same height it was originally hit. Over the entire flight, the work done by gravity and the work done by air resistance, respectively, are
zero, negative
