13.2.A.1Multiple Choice
Which statement best defines work in physics?
Select A, B, C, or D to check your answer.
Directions:Work each problem on your own paper first. For multiple choice, select A, B, C, or D. You will see right away whether you are correct. If you miss, you will see the most likely reason, and you can try again. For short response, type your answer, then compare it with the model solution. Questions mix the five essential knowledge statements of Topic 3.2 — work as energy transfer and conservative versus nonconservative forces, the sign of work, W = Fd cos θ and the parallel component, the work-energy theorem, and work as the area under an F versus displacement graph. Use g = 10 m/s². Round decimals to the nearest hundredth unless noted otherwise.
Which statement best defines work in physics?
Select A, B, C, or D to check your answer.
A 2 kg ball is carried from point A to point B, which is 3 m higher than A. First it is lifted straight up. Then it is carried along a long, winding path that also ends at B. (a) Find the work done by gravity on the ball along the straight path. (b) Find the work done by gravity along the winding path. (c) Find the work done by gravity if the ball is then carried from B back to A by any path. What does this say about gravity?
The work done by which of the following forces depends on the path taken between the starting and ending positions?
Select A, B, C, or D to check your answer.
A constant 20 N force acts on a crate while the crate moves 3.0 m along a straight line. Find the work done by the force when the angle between the force and the displacement is (a) 0°, (b) 90°, and (c) 120°. (cos 120° = −0.5)
A ball is thrown straight up. During the time the ball is rising, the work done on the ball by gravity is
Select A, B, C, or D to check your answer.
A 5 kg crate is pushed across a floor where the kinetic friction force is 15 N. It must go from point P to point Q. Taking the straight route, the crate slides 6 m. Taking a longer route around some furniture, it slides 10 m. (a) Find the work done by friction on the straight route. (b) Find the work done by friction on the longer route. (c) Can a potential energy be defined for the friction force? Explain.
A student holds a 10 kg box motionless at arm's length for 20 s. How much work does the student do on the box during this time?
Select A, B, C, or D to check your answer.
An 800 kg elevator is raised 10 m by a cable at constant speed. (a) Find the work done on the elevator by the cable's tension. (b) Find the work done on the elevator by gravity. (c) Find the net work, and explain how it agrees with the elevator's motion.
A 10 N force pulls a crate 4.0 m horizontally across a floor. The force is directed 60° above the horizontal. How much work does the force do on the crate? (sin 60° = 0.87, cos 60° = 0.50)
Select A, B, C, or D to check your answer.
A 50 N force pulls a cart 8.0 m along level ground. The force is directed 30° above the horizontal. (a) Find the work done by the force. (b) Find the vertical component of the force. How much work does it do? (c) If the angle were increased to 60° with the same force and distance, what would the work be? (cos 30° = 0.866, cos 60° = 0.50)
A ball on a string moves in a horizontal circle at constant speed. How much work does the tension in the string do on the ball during one full revolution?
Select A, B, C, or D to check your answer.
A 6 kg block slides 5.0 m down a frictionless incline that makes a 30° angle with the horizontal. (a) Find the component of gravity parallel to the incline. (b) Find the work done by gravity. (c) Find the work done by the normal force. (sin 30° = 0.50)
A block slides down a frictionless incline. Which of the following forces acting on the block does zero work?
Select A, B, C, or D to check your answer.
A 2 kg cart is moving at 3 m/s when a constant 8 N net force acts on it in the direction of its motion for a distance of 2.0 m. (a) Find the net work done on the cart. (b) Find the cart's initial and final kinetic energies. (c) Find the cart's final speed.
A 2 kg cart starts from rest, and the net work done on it is 36 J. What is the cart's final speed?
Select A, B, C, or D to check your answer.
A 1000 kg car traveling at 20 m/s skids to a stop on a level road. The friction force on the car is a constant 8000 N. (a) Find the car's initial kinetic energy. (b) How much energy is dissipated by friction? (c) How far does the car skid? (d) If the car had been going 40 m/s, how far would it skid?
A 3 kg block slides across a rough floor and slows from 5 m/s to 3 m/s. How much work does friction do on the block?
Select A, B, C, or D to check your answer.
The graph shows the force component parallel to the displacement acting on an object as it moves from x = 0 to x = 4 m. The force increases steadily from 0 N to 12 N. (a) Find the work done from x = 0 to x = 4 m. (b) Find the work done from x = 0 to x = 2 m. (c) Find the work done from x = 2 m to x = 4 m.
The graph shows the force component parallel to the displacement as a function of position for an object moving from x = 0 to x = 6 m. What is the total work done by the force over this interval?
Select A, B, C, or D to check your answer.
A 3 kg object starts from rest at x = 0. The graph shows the force component parallel to its displacement: the force rises from 0 N to 8 N over the first 2 m, stays at 8 N until x = 5 m, then is −4 N from x = 5 m to x = 7 m. (a) Find the work done from x = 0 to x = 5 m. (b) Find the work done from x = 5 m to x = 7 m. (c) Find the total work. (d) Find the object's speed at x = 7 m.