AP Physics I: Test 2 (Marzloff)

When does a car have a negative velocity and positive acceleration?

-x direction, decreasing in speed velocity and acceleration in opposite directions=decreasing speed

a 50 N crate sits on a horizontal floor where the coefficient of static friction between the crate and the floor is 0.50. A 20 N force is applied to the crate acting to the right. What is the resulting static friction force acting on the crate.

20 N to the left

Block A is placed on a rough surface inclined at an angle θ above the horizontal. A taut string connects block A over a pulley to block B, which hangs from the string, as shown below. The masses of blocks A and B are MA and MB, respectively. At time t=0, block A is sliding up the slope as block B falls, and the blocks are both slowing down. Assume that the mass and friction of the pulley are negligible.

20N

Block A of mass 4m is attached by a light string to block B of mass 2m. The string passes over a pulley with negligible friction and of negligible mass. Block A is held a distance h above the ground, as shown. The blocks are released from rest, and block A reaches the ground two seconds later. The value of h is most nearly

6.7 m

A car drives at steady speed around a perfectly circular track.

Both the acceleration and net force on the car point inward.

A 3kg object experiences a rightward horizontal acceleration of 6m/s2 as it slides to the right across a rough, horizontal surface. The table above contains the label and magnitude of four forces exerted to the right or left on the object that represent measurements from an experiment as the object accelerates. Which pair of opposing forces in which directions could be responsible for the acceleration of the object?

F3 to the right and F2 to the left

Three blocks are sliding together to the right along a surface of negligible friction when a force with magnitude Fext is exerted to the left on the rightmost block, as shown in the figure. The masses of the blocks are indicated in the figure. If the force is exerted for a time Δt, what is the change in velocity of the center of mass of the three-block system?

Fext/6mΔt

Three boxes are pulled to the left by strings with negligible mass on a horizontal surface, as shown above. The masses of the boxes are m1, m2, and m3, where m3>m2>m1. Friction between the boxes and the surface is negligible. The figure below shows force diagrams for each box. Which of the following is a correct ranking of the normal forces Fn1, Fn2, and Fn3 exerted on the boxes?

Fn3>Fn2>Fn1

A 1kg block is placed near the top of an inclined plane that is at an angle of 30 degrees with respect to the ground, as shown above. By correctly determining the effect of gravity, a student predicts that the acceleration of the block will be 5m/s2. After allowing the block to slide down the inclined plane, the student finds that the acceleration is actually 4m/s2. What type of force did the student most likely not account for when predicting the acceleration of the block, and what is the magnitude of that force?

Force of friction of approximately 1N

A hockey player uses a hockey stick to hit a puck such that the stick provides an applied force on the puck. The puck travels for distance of 0.85m while experiencing the force from the stick. The puck leaves the stick with a speed of 8.0m/s and travels at constant speed in a straight line along the horizontal ice for a distance of 12m. The frictional force between the puck and the ice surface is negligible. How does the magnitude of the force exerted by the stick on the puck Fpuck,stick compare to the magnitude of the force exerted by the puck on the stick Fstick,puck at the time interval in which the stick is in contact with the puck?

Fpuck,stick=Fstick,puck

An object of mass M is dropped near the surface of Earth such that the gravitational field provides a constant downward force on the object. Which of the following describes what happens to the center of mass of the object-Earth system as the object falls downward toward Earth?

It does not move.

A toy car has a battery-powered fan attached to it such that the fan creates a constant force that is exerted on the car so that it is propelled in the opposite direction in which the fan blows air. The car has a carriage that allows a student to attach objects of different masses, as shown above. The fan has only one speed setting. All frictional forces are considered to be negligible. Which of the following procedures could be used to determine how the mass of the fan-car-object system affects the acceleration of the system?

Measure the mass of the system using a balance, activate the fan, measure the distance traveled by the system at a known time by using a stopwatch, and repeat the experiment for several trials with different objects added to the carriage.

A block is placed on an inclined plane and remains stationary, as shown in the figure above. A student claims, "The block remains stationary because as gravity tries to pull the block down the ramp, the block exerts an equal and opposite force on itself up the ramp." Is the student's claim correct? Justify your answer.

No. Newton's third law states the block cannot exert a force on itself.

A block slides with constant velocity down a rough inclined plane that makes an angle of θ with the horizontal. It experiences three forces: gravitational (Fg), normal (FN), and frictional (Ff). Which of the following gives the magnitude of the net force on the block?

Since the object is not accelerating, it experiences no net force.

Two ice skaters, Skater X and Skater Y, are at rest on a horizontal surface made of ice. The friction between the ice and the skaters is negligible. Skater X, who has a smaller mass than Skater Y, pushes Skater Ysuch that Skater Y travels with a speed of 2vo to the right. Which of the following indicates the direction of the velocity of Skater X and the direction of the velocity of the center of mass of the two-skater system after the push?

Skater X's velocity is directed to the left the center of mass is zero

Three blocks with masses m1, m2, and m3 are attached by strings, as shown in the figure above. The coefficient of friction between each of the blocks and the horizontal surface is μ. The tension in the left and right strings is T2 and T1, respectively. If the acceleration of the blocks is a, which of the following expressions is equal to T2 ?

T1−m2a−μm2g

Three boxes are pulled to the left by strings with negligible mass on a horizontal surface, as shown above. The masses of the boxes are m1, m2, and m3, where m3>m2>m1. Friction between the boxes and the surface is negligible. The figure below shows force diagrams for each box. Given that m3>m2>m1, how do the force F and string tensions TA and TB compare?

TB<TA<F

A 1500kg car traveling along a road is hit by a 0.1kgrock that creates a small crack in the car's windshield. Which of the following describes the interaction between the windshield and the rock?

The car exerts a force on the rock, and the rock exerts a force on the car. The two forces are equal in magnitude.

Two astronauts of identical mass are connected by a taut cable of negligible mass, as shown in the figure above, and are initially at rest with respect to a nearby space station. Astronaut Y pulls on the cable toward herself with considerable force. Which of the following describes the direction of the velocity of the center of mass of the two astronauts after Astronaut Y pulls on the cable?

The center of mass does not move.

Two students, Student X and Student Y, stand on a long skateboard that is at rest on a flat, horizontal surface, as shown. In order to get the student-student-skateboard system to accelerate, Student X claims that Student Y should apply a force on Student X while both students stand on the skateboard. Which of the following statements is true regarding the claim made by Student X?

The claim is incorrect because both students are internal to the student-student-skateboard system, and internal forces within a system cannot cause the system to accelerate.

Two objects, X and Y, move toward one another and eventually collide. Object X has a mass of 2M and is moving at a speed of 2v0 to the right before the collision. Object Y has a mass of Mand is moving at a speed of v0 to the left before the collision. Which of the following describes the magnitude of the forces F the objects exert on each other when they collide?

The force exerted by X on Y is F to the right, and the force exerted by Y on X is F to the left.

Students connect a spring scale to a block on a rough horizontal surface. The students use the spring scale to measure the magnitude of the horizontal force needed to pull the block at a constant speed. Which of the following statements explains why two forces exerted between objects are equal in magnitude?

The frictional forces that the block and the surface exert on each other, because objects always exert forces of equal magnitude on each other.

A satellite orbits Earth. The only force on the satellite is the gravitational force exerted by Earth. How does the satellite's acceleration compare to the gravitational field at the location of the satellite? Select two answers.

The gravitational field and the acceleration point in the same direction. The magnitudes of the acceleration and the gravitational field strength are equal.

A 5kg object is released from rest near the surface of a planet such that its gravitational field is considered to be constant. The mass of the planet is unknown. After 2s, the object has fallen 30m. Air resistance is considered to be negligible. What is the gravitational force exerted on the 5kg object near the planet's surface?

The kinematics equation that relates distance, time, and acceleration is used to calculate the acceleration of the object as it falls near the planet's surface: x=x0+vx0t+12axt2∴a=2xt2=2(7.5m)(1s)2=15 m/s2. Using the acceleration, the equation for weight can be used to calculate the weight of the 5 kg object: ΣF⃗ =ma=(5kg)(15m/s2)=75N.

A spring-loaded launcher has a mass of 0.60 kg and is placed on a platform 1.2m above the ground. The force of friction is negligible between the platform and the launcher. The launcher fires a 0.30kg ball that lands a distance D to the right of the platform, as shown in the diagram above

The launcher will fall off the platform and land D2 to the left of the platform because the launcher is twice the mass of the ball.

A falling skydiver opens his parachute. A short time later, the weight of the skydiver-parachute system and the drag force exerted on the system are equal in magnitude. Which of the following statements predicts the motion of the skydiver at this time?

The skydiver is moving downward with constant speed.

A student sets up an experiment to determine the inertial mass of a cart. The student has access to the following measurement equipment: a spring scale, a meterstick, and a stopwatch. The student uses the spring scale to pull the cart starting from rest along a horizontal surface such that the reading on the spring scale is always constant. All frictional forces are negligible. In addition to the spring-scale reading, which two of the following quantities could the student measure with the available equipment and then use to determine the inertial mass of the cart? Select two answers.

The total distance traveled by the cart after it has been in motion The time during which the cart is in motion

Three boxes are pulled to the left by strings with negligible mass on a horizontal surface, as shown above. The masses of the boxes are m1, m2, and m3, where m3>m2>m1. Friction between the boxes and the surface is negligible. The figure below shows force diagrams for each box. Students attach a force probe in the middle of string A to measure TA and then use a different force probe to provide the applied force F to the box of mass m1. With the box of mass m3 held in place by one student, a second student pulls to the left on the force probe that provides the applied force F. As the second student pulls with a steady force, and with the boxes remaining at rest, the following pairs of readings from the two force probes are recorded at different times. Based on the measurements above, how do the magnitudes of the two force quantities compare?

The two quantities agree within experimental uncertainty but do not exactly agree numerically.

A hockey player uses a hockey stick to hit a puck such that the stick provides an applied force on the puck. The puck travels for distance of 0.85m while experiencing the force from the stick. The puck leaves the stick with a speed of 8.0m/s and travels at constant speed in a straight line along the horizontal ice for a distance of 12m. The frictional force between the puck and the ice surface is negligible. Which of the following statements best describes the force or forces exerted on the puck after it is hit by the stick and slides on the ice?

There is no frictional force exerted on the puck, and the gravitational force and normal force are exerted on the puck and are equal in magnitude.

Which of the following experiments could be used to determine the inertial mass of a block?

Use a spring scale to exert a force on the block. Measure the acceleration of the block and the applied force.

What points towards the center of the circle in uniform circular motion?

acceleration, net force velocity=perpendicular

In the setup shown in the figure, two blocks of equal mass M are at rest but are just about to slip. Also shown is a free-body diagram for the block on top of the table. In this setup, the coefficient of static friction between the table and the block resting upon it must be

at least 1.0

A child whirls a ball in a vertical circle. Assuming the speed of the ball is constant, when would the tension in the cord connected to the ball be greatest?

at the bottom of the circle

You drop a rock off a bridge. When the rock has fallen 4 m, you drop a second rock. As the two rocks continue to fall, what happens to their velocities?

both increase at the same rate both under influence of gravity

Suppose an object is accelerated by a force of 100 N. Suddenly a second force of 100 N in the opposite direction is exerted on the object, so that the forces cancel. The object

continues at the velocity it had before the second force was applied (1st Law)

A person kicks a ball into the air with a force F0. The figure shows the position of the ball at various times. What is the net force on the ball and its acceleration at the highest point shown?

force=mg+Fo acceleration=0

The normal force on an extreme skier descending a very steep slope can be zero if

he leaves the slope the slope is vertical

A bear sling is used in some national parks for placing backpackers' food out of the reach of bears. As the backpacker raises the pack by pulling down on the rope, the force F needed

increases but the rope always sags where the pack hangs

A person stands on a scale in an elevator. His apparent weight will be the greatest when the elevator

is accelerating upward

The Moon does not crash into the Earth because

it is free falling but it has a high tangential velocity

you drive 4km at 30km/h and then another 4km at 50km/h. What is you avg speed for the whole 8-km trip?

less than 40 km/h takes car much longer to drive 4km at 30 km/h

To pull an old stump out of the ground, you and a friend tie two ropes to the stump. You pull on it with a force 500 N north while your friends with a force of 450 N northwest. The total force from the two ropes is.

less than 950 N

When a skier skis down a hill, the normal force exerted on the skier by the hill is

less than the weight of the skier

Three boxes are pulled to the left by strings with negligible mass on a horizontal surface, as shown above. The masses of the boxes are m1, m2, and m3, where m3>m2>m1. Friction between the boxes and the surface is negligible. The figure below shows force diagrams for each box. A student is trying to determine the tensions in the strings connecting the boxes. If the acceleration of the system and the pulling force F are known, which of the following pairs of equations could be used to find the tensions?

m3a3=TB and m2a2=TA−TB

A truck is traveling horizontally to the right. When the truck starts to slow down, the crate on the (frictionless) truck bed starts to slide. In what direction could the net force be on the crate?

no direction. the net force is zero

A ball is dropped from the top of a tall building. At the same instant, a second ball is thrown upward from the ground level. When the two balls pass one another, one on the way up, the other on the way down, compare the magnitudes of their acceleration:

the acceleration of both balls is the same

While driving around a sharp right turn, you find yourself pressing against the car door. What is happening?

the door is exerting a rightward force on you

You are trying to push your stalled car. Although you apply a horizontal force of 400N to the car, it doesn't budge, and neither do you. Which forces must also have a magnitude of 400 N?

the force exerted by the car on you the friction force exerted by the car on the road the friction force exerted by the road on you

A golf ball is hit with a golf club. While the ball flies through the air, which forces act on the ball? Neglect air resistance.

the force gravity acting on the ball

What causes a gondola boat to move forward?

the force the water exerts on the paddle

You are pushing a heavy box across a rough floor. When you are initially pushing the box and it is accelerating,

the force you exert on the box is equal to the force of the box pushing back on you (3rd Law)

A man is able to move a large truck because

the ground exerts a greater friction force on him than it does on the truck

At time t=0 an object is traveling to the right along the +x axis at a speed of 10.0 m/s with acceleration -2.0 m/s^2. Which statement is true?

the object will slow down, momentarily stopping, then pick up speed moving to the left opposite directions mean slow to a stop, acceleration is constant so it only stop momentarily before moving left

A ball is thrown straight up. What are the velocity and acceleration of the ball at the highest point in its path?

v=0, a=9.8 m/s^2 down

The amusement park ride shown above takes riders straight up a tall tower and then releases an apparatus holding seats. This apparatus free-falls back to Earth and is stopped safely right above the ground. Which of the following indicates the magnitude of the gravitational force exerted on a rider of mass m on the way up and on the way down?

way up: equal to mg way down: equal to mg

A ball is thrown downward at a speed of 20 m/s. Choosing the +y axis pointing up and neglecting air resistance, which equation could be used to solve for other variables? (g=9.8 m/s^2 downward)

y=yo+(-20m/s)t-1/2gt^2 v^2=(20m/s)^2-2g(y-yo)