Physics Midterm

A ball is suspended by a lightweight string, as shown in the figure above. The ball is displaced to position 1 and released. The four labeled positions are evenly spaced along the arc of the ball's motion. Between which adjacent pairs of positions is the change in kinetic energy of the ball greatest?

1 and 2

A 2 kg block, starting from rest, slides 20 m down a frictionless inclined plane from X to Y, dropping a vertical distance of 10 m as shown above. The speed of the block at point Y is most nearly

14 m/s

An object starts from rest and slides with negligible friction down an air track tipped at an angle θ from the horizontal. A student records values of the object's position along the track at various times. The value of θ can best be determined from which of the following?

The slope of a graph of position as a function of the square of time

A 50.0 N box is at rest on a horizontal surface. The coefficient of static friction between the box and the surface is 0.50, and the coefficient of kinetic friction is 0.30. A horizontal 20.0 N force is then exerted on the box. The magnitude of the acceleration of the box is most nearly

0 m/s2

A 50 kg athlete running at speed v grabs a light rope that hangs from a 10-meter-high platform and swings to a maximum of 1.8 m above the ground. Later, a 100 kg athlete, running at the same speed, grabs a similar rope hanging from a 5-meter-high platform. What is the maximum height to which the 100 kg athlete swings?

1.8 m

A ball is thrown with an initial speed of 20 m/s at an angle of 60° to the ground. If air resistance is negligible, what is the ball's speed at the instant it reaches its maximum height from the ground?

10 m/s

An object of mass 10 kg is released from rest above the surface of a planet such that the object's speed as a function of time is shown by the graph above. The force due to gravity exerted on the object is most nearly

35 N

A 10 kg block is attached to a light cord that is wrapped around the pulley of an electric motor, as shown above. At what rate is the motor doing work when it is pulling the block upward with an instantaneous speed of 3 m/s and an upward acceleration of 2 m/s2 ?

360 W

A 12 kg box sliding on a horizontal floor has an initial speed of 4.0 m/s. The coefficient of friction between the box and the floor is 0.20. The box moves a distance of 4.0 m in 2.0 s. The magnitude of the change in momentum of the box during this time is most nearly...

48 kg m/s

Three identical blocks each take a different path from a height h to the ground. Block A is released from rest and falls vertically. Block B is released from rest and slides down a frictionless incline. Block C is projected horizontally with an initial speed v. Which block has the greatest speed just before hitting the ground?

C

Blocks X and Y are connected by a string that passes over a pulley, as shown in the figure. Block Y has more mass than Block X. The string and pulley have negligible mass, and the pulley rotates with negligible friction. After the blocks are released from rest, what happens to the mechanical energy Emech of the system consisting of the two blocks and Earth?

Emech remains constant.

Some students want to calculate the work done by friction as an object with unknown mass moves along a straight line on a rough horizontal surface. The students have a force probe, a meterstick, and a stopwatch. Which of the following will allow the students to take the measurements needed to calculate the work done by friction?

Pulling the block at an unknown constant speed with the force probe for a measured distance

A ball is thrown straight up in the air. When the ball reaches its highest point, which of the following is true?

None of the above

A block moving to the right on a level surface with friction is pulled by an increasing horizontal force also directed to the right. As the applied force increases, which of the following is true of the normal force and the frictional force on the block?

Normal Force: remains constant Frictional Force: increases

The horizontal wire shown on the right in the figure above will break when the tension in it exceeds the value Tmax. What is the maximum mass M that the hanging object can have without the horizontal wire breaking? (Assume the wire on the left does not break prior to the horizontal wire breaking.)

Tmaxtanθg

The figure above shows the net force exerted on an object as a function of the position of the object. The object starts from rest at position x = 0 m and acquires a speed of 3.0 m / s after traveling a distance of 0.090 m. What is the mass of the object

0.030 kg

An experiment is conducted such that an applied force is exerted on a 2kg object as it travels across a horizontal surface. A graph of the net force exerted on the object as a function of the object's distance traveled is shown. How could a student use the graph to determine the work done by the applied force?

Calculate the area bound by the line of best fit and the horizontal axis from 0m to 3m.

A student is conducting an experiment to analyze the mechanical energy of a block-spring system. The student places a block of mass 2kg on a horizontal surface and attaches the block to a horizontal spring of negligible mass and spring constant 100N/m, as shown in the figure. There is negligible friction between the block and the horizontal surface. The other end of the spring is attached to a wall. The block-spring system is initially at the spring's equilibrium position. The student wants to collect data of the block-spring system that can be used to determine the work done on the spring by the block when the spring is compressed. Which of the following includes only the measuring devices that the student will need in order to collect the data?

Force probe and meterstick

A book is at rest on the top of a table. A student makes the following claim: "An attractive electromagnetic force is exerted on the book from the table, and this force can also be classified as the normal force." Which of the following statements correctly justifies the student's claim?

The claim is incorrect because the charged particles of the table exert an upward repulsive force on the charged particles of the book.

A ladder at rest is leaning against a wall at an angle. Which of the following forces must have the same magnitude as the frictional force exerted on the ladder by the floor?

The normal force exerted on the ladder by the wall

Two identical books are stacked on a table. A third identical book is then placed on top of the first two, causing an increase in the normal force exerted by the bottom book on the middle book. Which of the following is a correct explanation for the increase in this normal force?

The third book produces an additional downward force on the middle book, thus increasing the upward force exerted by the bottom book to maintain equilibrium.

A child slides from rest down slides A and B shown above. The slides are the same height, and the coefficient of friction between the slides and the child is the same. Which of the following compares the change ∆K in the kinetic energy of the child and the change ∆Uin the potential energy of the child-Earth system for the two slides?

∆KA > ∆KB; ∆UA = ∆UB

To analyze the characteristics and performance of the brakes on a 1500 kg car, researchers collected the data shown in the table above. It shows the car's speed when the brakes are first applied and the corresponding braking distance required to stop the car. The magnitude of the average braking force on the car is most nearly

12,000 N

A block is projected up a frictionless plane with an initial speed vo. The plane is inclined 30° above the horizontal. What is the approximate acceleration of the block at the instant that it reaches its highest point on the inclined plane?

5 m/s2 down the incline

A student wants to determine the coefficient of static friction μ between a block of wood and an adjustable inclined plane. Of the following, the minimum additional equipment the student needs to determine a value for μ is

protractor only