Physics 211 Getaneh Final
A person with mass 60kg is standing in an elevator that is accelerating upwards with an acceleration a=2. What is the net force on this person
120N
A store's sign has a mass of 20 kg and is 3.0 m long. It is uniform, so its center of gravity is at the center of the sign. It is supported horizontally by a small loose bolt attached to the wall at one end and by a wire at the other end, as shown in the figure. What is the tension in the wire?
230 N
A 1200 kg cannon suddenly fires a 100 kg cannonball at 35 m/s. What is the recoil speed of the cannon? Assume that frictional forces are negligible and the cannon is fired horizontally.
29 m/s
A ball is thrown with a velocity of 20 m/s at an angle of 60 above the horizontal. What is the horizontal component of its instantaneous velocity at the exact top of its trajectory?
10 m/s
A mobile is shown in the figure. The horizontal supports have negligible mass. Assume that all the numbers given in the figure are accurate to two significant figures. What mass M is required to balance the mobile?
36 g
Planet Z-34 has a mass equal to 1/3 that of Earth, a radius equal to 1/3 that of Earth. With g representing, as usual, the acceleration due to gravity on the surface of Earth, the acceleration due to gravity on the surface of Z-34 is
3g
A tiger is running in a straight line. If we double both the mass and speed of the tiger, the magnitude of its momentum will increase by what factor?
4
Two uniform solid spheres have the same mass, but one has twice the radius of the other. The ratio of the larger sphere's moment of inertia to that of the smaller sphere is
4
A force of 30 N stretches a very light ideal spring 0.73 m from equilibrium. What is the force constant (spring constant) of the spring?
41
An 8.0-g bullet is shot into a 4.0-kg block, at rest on a frictionless horizontal surface (see the figure). The bullet remains lodged in the block. The block moves into a spring and compresses it by 3.7 cm. The force constant of the spring is 2500 N/m. What was the initial speed v of the bullet?
460 m/s
You can swim in still water at the rate of 3km/h. How long will it take you to move 0.5km downstream in a river that flows at a rate of 3km/h?
5 min
It's more difficult to start moving a heavy carton from rest than it is to keep pushing it with constant velocity, because
Uk<Us
You are standing in a moving bus, facing forward, when you suddenly slide forward as the bus comes to an immediate stop. What force caused you to slide forward?
Velocity decreased
A net force F accelerates a mass m with an acceleration a. If the same net force is applied to mass 2m, then the acceleration will be
A/2
Consider a uniform hoop of radius R and mass M rolling without slipping. Which is larger, its translational kinetic energy or its rotational kinetic energy?
Both are equal
Three boxes are at rest on a level surface as shown. Forces applied to the boxes as shown. Which one is going to move in response to the applied force if the coefficient of static friction between the boxes and the floor is 0.1?
Box C
The graph of the figure shows the tensile stress as a function of the tensile strain in a certain wire. What does the slope of this graph give us for this wire
Young's modulus for the material of the wire
When you sit on a chair the resultant force on you is
Zero
action-reaction forces are
Equal in magnitude but point in opposite directions
You stand on an elevator that is moving upward with constant speed while standing on a bathroom scale. The reading on the scale is
Equal to your true weight, mg
Identical forces act for the same length of time on two different objects. The magnitude of the change in momentum of the lighter object is
Exactly equal to the magnitude of the change in momentum of the larger mass
Two small balls, A and B, attract each other gravitationally with a force of magnitude F. If we now double both masses and the separation of the balls, what will now be the magnitude of the attractive force on each one?
F
If an object remains at rest, then the sum of both the external torques and the external forces on the object must be zero
False
If the sum of both the external torques and the external forces on an object is zero, then the object must be at rest
False
If the sum of the external forces on an object is zero, then the sum of the external torques on it must also be zero.
False
Objects A and B both start at rest. They both accelerate at the same rate. However, object A accelerates for twice the time as object B. What is the distance travelled by object A compared to Object B?
Four times as far
You are trying to cross a river that flows due south with a strong current. You start out in your motorboat on the east bank desiring to reach the south West Bank directly from your starting point. You should head your motorboat
In a north westerly direction
Suppose an object is moving with constant acceleration. Make a statement concerning its motion with respect to time.
In equal times its velocity changes by equal amounts
A package of supplies is dropped from a plane, and one second later a second package is dropped. Neglecting air resistance, the distance between the falling packages will
Increase
An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. What happens to his angular momentum about the axis of rotation?
It does not change
Two wires are made out of the same metal, but one wire is twice as long as the other wire. Which wire will have the greatest elastic modulus?
It will be the same for both wires
An object of mass m is hanging by a string from the ceiling of an elevator. The elevator is moving upward, but slowing down. What is the tension in the string?
Less than mg
A solid sphere and a solid cylinder, both uniform and of the the same mass and radius, roll without slipping at the same forward speed. It is correct to say that the total kinetic energy of the solid sphere is
Less than the total kinetic energy of the cylinder
What is the quantity used to measure an objects resistance to rotational motion?
Moment of inertia
In the absence of an external force, a moving object will
Move with constant velocity
Two men, Joel and Jerry, push against a wall. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do.
Neither of them does any work.
Who has a greater weight to mass ratio, a person weighing 400 N or a person weighing 600 N?
Neither; their ratios are the same
If you blow up a balloon, and then release it, the balloon will fly away. This is an illustration of
Newton's third law
A constant net force acts on an object. Describe the motion of the object.
constant non-zero acceleration
The area under a curve in a velocity versus time graph gives
displacement
You are throwing a ball for the second time. If the ball leaves your hand with twice the velocity it had on your first throw, its horizontal range R (compared to your first serve) would be
four times as much
A person sits on a freely spinning lab stool that has no friction in its axle. When this person extends her arms,
her moment of inertia increases and her angular speed decreases
When an object experiences uniform circular motion, the direction of the net force
is directed toward the center of the circular path.
A irregularly shaped object that is 10m long is placed with each end on a scale. If the scale on the right reads 96N while the scale on the left reads 71N, how far from the left end is the center of gravity of this object?
5.7 m
A 1200 kg car is being raised at a constant speed if 25 cm/s by a crane, using a 20-m long steel cable that is 1.5 cm in diameter. Young's modulus for steel is 2.0x10^11 Pa. What is the change in length of the cable caused by the car?
6.7 mm
A truck is using a hook to tow a car whose mass is one quarter that of the truck. If the force exerted by the truck on the car is 6000 N, then the force exerted by the car on the truck is
6000N
The earth has radius R. A satellite of mass 100 kg is at a point 3R above the Earth's surface. Approximately, what is the satellites weight?
60N
A 3kg crate is being lifted with a cord upward with an acceleration of 2m/s. The net force on the crate is
6N
An aluminum wire is 2.0 m long and 2.0 mm in diameter supports a 10.0 kg fixture. What is the stress in the wire? Young's modulus for aluminum is 7.0x10^10 N/m^2
8.1x10^7
A block of mass m=9.0 kg and speed V is behind a block of mass M= 27 kg and speed of .50 m/s, as shown in the figure. The surface is frictionless, and the blocks suddenly collide and couple. After the collision, the blocks have a common speed of 0.90 m/s. How much kinetic energy of the blocks is lost due to collision?
8.6 J
How much work would a child do while pulling a 12-kg wagon a distance of 4.3 m with a 22 N force?
95 J
When is the angular momentum of a system constant?
Only when no net external torque acts on the system.
When is the average velocity of an object equal to the instantaneous velocity?
Only when the velocity is increasing at a constant rate
Which one has larger kinetic energy: a 500-kg object moving at 40 m/s or a 1000-kg object moving at 20 m/s?
The 500-kg object
Under what condition is average velocity equal to the average of the objects initial and final velocity?
The acceleration is constant
A rubber ball and a lump of clay have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The clay sticks to the wall. Which one of these objects experiences the greater momentum change?
The ball
Suppose a car is traveling west (-x direction) slows down as it approaches a traffic light. Make a statement concerning its acceleration
The car is decelerating, and its acceleration is positive
When a car is weighed, it is driven slowly on a horizontal floor over a scale that records a reading as the front wheels go over the scale, and then records a second reading as the rear wheels go over the scale. The weight of the car is equal to
The difference of the two weights
Suppose that an object travels from one point in space to another. Make a comparison between the displacement and the distance traveled.
The displacement is either less than or equal to the distance traveled.
Ignoring air resistance, the horizontal component of a projectile's acceleration
is zero
A uniform ball is released from rest on a no-slip surface, as shown in the figure. After reaching its lowest point, the ball begins to rise again, this time on a frictionless surface. When the ball reaches its maximum height on the frictionless surface, it is
lower than when it was released.
If the position versus time graph of an object is a vertical line, the object is
moving with infinite speed
Suppose a uniform solid sphere of mass M and radius R rolls without slipping down an inclined plane starting from rest. The linear velocity of the sphere at the bottom of the incline depends on
neither the mass nor the radius of the sphere.
Two objects attract each other gravitationally. If the distance between their centers is cut in half, the gravitational force
quadruples
For general projectile motion, the horizontal component of a projectile's velocity
remains a non-zero constant
You are in a train traveling on a horizontal track and notice that a piece of luggage starts to slide directly toward the front of the train. From this observation, you can conclude that this train is
slowing down
Two equal-magnitude forces are applied to a door at the doorknob. The first force is applied perpendicular to the door, and the second force is applied at 30° to the plane of the door. Which force exerts the greater torque about the door hinge?
the first force (applied perpendicular to the door)
Two forces produce equal torques on a door about the door hinge. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force has a greater magnitude?
the first force (at the midpoint)
When a car goes around a circular curve on a horizontal road at constant speed, what force causes it to follow the circular path?
the friction force from the road
An object moves in a circular path at a constant speed. Compare the direction of the object's velocity and acceleration vectors.
The vectors are perpendicular
A bullet is fired horizontally, and at the same instant a second bullet is dropped from the same height. Ignore air resistance. Compare the times of fall of the two bullets.
They hit at the same time
In a collision between two unequal masses, which mass receives a greater magnitude impulse
They receive equal impulses
A car goes around a curve of radius r at a constant speed v. What is the direction of the net force on the car?
Toward the center of the circle
Consider a solid uniform sphere of radius R and mass M rolling without slipping. Which form of its kinetic energy is larger, translational or rotational?
Translational kinetic energy is larger.
A 60.0-kg man stands at one end of a 20.0-kg uniform 10.0-m long board. How far from the man is the center of mass (or center of gravity) of the man-board system?
1.25m
How large must the coefficient of static friction between the tires and the road be if a car is to round a level curve of radius 100m at a speed of 20 m/s
0.4
Three objects are moving along a straight line as shown in the figure. Taking the positive direction to be to the right, what is the total momentum of this system?
-14.0 kg • m/s
A forklift pushes a 100-kg crate, starting from rest, with a horizontal force of magnitude F. The graph in the figure shows the x component of this force as a function of time. What is the instantaneous velocity of the crate at time t = 10 s?
-75 cm/s
A rocket moves through empty space in a straight line with constant speed. It is far from the gravitational effect of any star or planet. Under these conditions, the force that must be applied to the rocket in order to sustain its motion is
0
You carry a 7.0 kg bag of groceries 1.2 m above the ground at constant speed across a 2.7 m room. How much work do you do on the bag in the process?
0 J
A 320g air track cart traveling at 1.25 m/s suddenly collides elastically with a stationary 270-g cart. What is the speed of the 320-g cart just after collision?
0.11 m/s
A 1000kg car is slowly picking up speed as it goes around a horizontal unbanked curve whose radius is 100m. The coefficient of static friction between the two tires and the road is 0.35. At what speed will the car begin to skid sideways?
19 m/s
A uniform 40-N board supports two children weighing 500 N and 350 N. If the support is at the center of the board and the 500-N child is 1.5 m from its center, how far is the 350-N child from the center?
2.1 m
An object that weighs 75N is pulled on a horizontal surface by a horizontal pull of 50 N to the right. The friction force on this object is 30 N to the left. What is the acceleration of this object?
2.6
A uniform rod weighs 40 N and is 1.0 m long. It is hinged to a wall at the left end, and held in a horizontal position at the right end by a vertical string of negligible weight, as shown in the figure. What is the magnitude of the torque due to the string about a horizontal axis that passes through the hinge and is perpendicular to the rod? The hinge is very small with negligible friction.
20 N ∙ m
Tensile strain is
The ratio of the change in length to the original length
A rocket explodes into two fragments, one 25 times heavier than the other. The magnitude of the momentum change of the lighter fragment is
The same as the momentum change of the heavier fragment.
The area under a curve in an acceleration versus time graph gives
Change in velcoity
A 20-ton truck collides with a 1500-lb car and causes a lot of damage to the car. Since a lot of damage is done on the car
The force on the truck is equal to the force on the car.
Consider two less-than-desirable options. In the first you are driving 30 mph and crash head-on into an identical car also going 30 mph. In the second option you are driving 30 mph and crash head-on into a stationary brick wall. In neither case does your car bounce back from the thing it hits, and the collision time is the same in both cases. Which of these two situations would result in the greater impact force on your car?
The force would be the same in both cases
The figure shows scale drawings of four objects, each of the same mass and uniform thickness, with the mass distributed uniformly. Which one has the greatest moment of inertia when rotated about an axis perpendicular to the plane of the drawing at point P
The moment of inertia is the same for all the objects
An object is moving to the left at a constant velocity, what can one conclude?
The net force applied to the object is zero
If the acceleration vector of an object is directed anti-parallel to the velocity vector ,
The object is slowing down
If the acceleration of an object is always directed parallel to its velocity
The object is turning
An object of mass m sits on a flat table. The Earth pulls on this object with force mg, What is the reaction force?
The object pulling upward on the Earth with force mg.
An object of mass m sits on a flat table. The Earth pulls on this object with force mg, which we will call the action force. What is the reaction force?
The object pulling upward on the Earth with force mg.
The slope of a velocity versus time graph gives
acceleration
Action-Reaction forces
always act on different objects
An object is moving with constant non-zero velocity. Which of the following statements about it must be true?
the net force on the object is zero
Swimmers at a water park have a choice of two frictionless water slides, as shown in the figure. Although both slides drop over the same height h, slide 1 is straight while slide 2 is curved, dropping quickly at first and then leveling out. How does the speed v1 of a swimmer reaching the bottom of slide 1 compare with v2, the speed of a swimmer reaching the end of slide 2?
v1 = v2
