Exam 5: Applying Newtons Laws

Friction: You push downward on a box at an angle 25° below the horizontal with a force of 750 N. If the box is on a flat horizontal surface for which the coefficient of static friction with the box is 0.76, what is the mass of the heaviest box you will be able to move?

General questions: Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with an unchanging velocity? _f is the force of the floor on the person and _g is the force of gravity on the person.

Newton's second law: Bumpers on cars are not of much use in a collision. To see why, calculate the average force a bumper would have to exert if it brought a 1200-kg car (a so-called compact model) to a rest in 15 cm when the car had an initial speed of 2.0 m/s (about 7.2 km/h). (Bumpers are built with springs that compress to provide a stopping force without, hopefully, denting the metal.)

Slanted surfaces with friction: A 200 g hockey puck is launched up a metal ramp that is inclined at a 30° angle. The coefficients of static and kinetic friction between the hockey puck and the metal ramp are μ_s = 0.40 and μ_k = 0.30, respectively. The puck's initial speed is 63 m/s. What vertical height does the puck reach above its starting point?

Equilibrium: The figure shows two forces acting on an object, with magnitudes and What third force will cause the object to be in equilibrium (acceleration equals zero)?

Friction: A 150-N box is being pulled horizontally in a wagon accelerating uniformly at 3.00 m/s². The box does not move relative to the wagon, the coefficient of static friction between the box and the wagon's surface is 0.600, and the coefficient of kinetic friction is 0.400. The friction force on this box is closest to

General questions: An object is moving forward with a constant velocity. Which statement about this object MUST be true?

Slanted surfaces with friction: A 6.0 kg box slides down an inclined plane that makes an angle of 39° with the horizontal. If the coefficient of kinetic friction is 0.19, at what rate does the box accelerate down the slope?

Multiple-object systems without friction: Two objects having masses m₁ and m₂ are connected to each other as shown in the figure and are released from rest. There is no friction on the table surface or in the pulley. The masses of the pulley and the string connecting the objects are completely negligible. What must be true about the tension T in the string just after the objects are released?

Friction: In a shuffleboard game, the puck slides a total of before coming to rest. If the coefficient of kinetic friction between the puck and the horizontal board is 0.28, what was the initial speed of the puck?

Air resistance: A ship is being pulled through a harbor at constant velocity by two tugboats as shown in the figure. The lines attached to the two tugboats have the same tension of 200,000 N. Each line makes an angle of 28.0° with the direction the ship is being towed. What is the magnitude of the drag force due to the water on the ship?

Multiple-object systems without friction: Two unequal masses M and m (M > m) are connected by a light cord passing over a pulley of negligible mass, as shown in the figure. When released, the system accelerates. Friction is negligible. Which figure below gives the correct free-body force diagrams for the two masses in the moving system?

Air resistance: Suppose the force of the air drag on an object is proportional to the speed of the object and in the direction opposite the object's velocity. If you throw an object upward, the magnitude of its acceleration is greatest

Uniform circular motion: A new roller coaster contains a loop-the-loop in which the car and rider are completely upside down. If the radius of the loop is with what minimum speed must the car traverse the loop so that the rider does not fall out while upside down at the top? Assume the rider is not strapped to the car.

Multiple-object systems with friction: Two boxes are connected by a weightless cord running over a very light frictionless pulley as shown in the figure. Box A, of mass 8.0 kg, is initially at rest on the top of the table. The coefficient of kinetic friction between box A and the table is 0.10. Box B has a mass of 15.0 kg, and the system begins to move just after it is released. (a) Draw the free-body diagrams for each of the boxes, identifying all of the forces acting on each one. (b) Calculate the acceleration of each box. (c) What is the tension in the cord?

Uniform circular motion: A car travels at a steady 40.0 m/s around a horizontal curve of radius 200 m. What is the minimum coefficient of static friction between the road and the car's tires that will allow the car to travel at this speed without sliding?

General questions: Suppose you are playing hockey on a new-age ice surface for which there is no friction between the ice and the hockey puck. You wind up and hit the puck as hard as you can. After the puck loses contact with your stick, the puck will

Multiple-object systems with friction: Block A of mass 5.0 kg and block X are attached to a rope which passes over a pulley, as shown in the figure. An 80-N force P is applied horizontally to block A, keeping it in contact with a rough vertical face. The coefficients of static and kinetic friction between the wall and block A are μ_s = 0.40 and μ_k = 0.30. The pulley is light and frictionless. The mass of block X is adjusted until block A moves upward with an acceleration of 1.6 m/s². What is the mass of block X?

General questions: Two objects, each of weight W, hang vertically by spring scales as shown in the figure. The pulleys and the strings attached to the objects have negligible weight, and there is no appreciable friction in the pulleys. The reading in each scale is

Multiple-object systems without friction: A series of weights connected by very light cords are given an upward acceleration of 4.00 m/s² by a pull P, as shown in the figure. A, B, and C are the tensions in the connecting cords. The pull P is closest to