 Phyllis Fleming Physics Physics 104
 Review - Newton's Laws
 1 The same constant net force acts on two different objects. A plot of velocity as a function of time for the two objects is given in Fig. 1 below. The graph labelled A is for object A; the one labelled B is for object B. The mass of object A is 2.0 kg. Find (a) the acceleration of object A, (b) the acceleration of object B, (c) the mass of object B, and (d) the magnitude of the net force. 2 An object of mass m, resting on a horizontal frictionless surface is acted upon by an applied force F, the normal force of the surface FN and the gravitational attraction of the earth Fg, as shown in Fig. 2 below. Find Fg, FN and the acceleration of the object when (a) F = 12 N and m = 2.0 kg, (b) F = 24 N and m = 2.0 kg, (c) F = 12 N and m = 1.0 kg. Take g = 10 m/s2. 3 In Fig. 2 above, the surface now exerts a frictional force of 4.0 N on the object when it is in motion. If the mass of the object m = 2 kg, find the acceleration of the object when (a) F = 12 N and (b) F = 24 N.
 4 Two objects of mass mA = 2.0 kg and mB = 4.0 kg rest on a frictionless surface (Fig. 3 below). An applied force F = 12 N acts on object A, as shown in Fig. 3. Find (a) the acceleration of the objects, (b) the force FAB of object B on A and (c) the force FBA of object A on B. 5 A rope is attached to a hook on a wall. You pull on the rope, but it does not move. Discuss the forces acting on the hook, the rope, and you. Which of these forces are Newton third law of motion forces?
 6 The two objects in Fig. 3 above are now connected by a massless string between A and B, string 1, and pulled to the right by exerting a force of 12 N to the right through another massless string, string 2, attached to block B. Find (a) the acceleration of the blocks and (b) the tension in string 1.
 7 (a) An object of mass m = 3.0 kg is set into motion vertically and then raised with a constant velocity of 3.0 m/s. What applied force F is needed? (b) The object is now given an upward acceleration of 3.0 m/s2. Now what applied force is needed? Take g = 10 m/s2.
 8 A system consisting of a rope of mass 0.10 kg between two blocks each of mass 0.10 kg is lifted by an applied force F = 9.0 N (Fig. 4 below). (a) Find the acceleration of the system. Find the tension at (b) the top of the rope, and (c) the bottom of one-fifth of the rope. Take g = 10 m/s2. 9 A block is pulled along a rough horizontal surface. Figure 5 below is a plot of the applied force F as a function of the acceleration of the block Find (a) the force that must be applied to move the block with constant velocity, (b) the mass of the block, (c) the force that must be applied to give the block an acceleration of 1.0 m/s2. (d) Suppose the experiment is repeated with a block of a greater mass. If the new block is pulled along the same surface, how will this change the graph? (e) Suppose the experiment is repeated with the original block, changing only the surface on which the block is pulled. How will this change the graph? 10 A block of mass m = 2.0 kg is moved to the right on a horizontal surface by a force of 26 N. The coefficient of kinetic friction µk between the surface and the object is 1/5. (a) Draw the object and show all of the forces acting on it. Find (b) the frictional force on the block and (c) the acceleration of the block. Take g = 10 m/s2.
 11 Repeat problem 10 when the applied force makes an angle of 22.6o above the horizontal.
 12 An object of mass m = 3.0 kg accelerates down a frictionless inclined plane that makes an angle of 370 with the horizontal. (a) Show all the forces acting on the object. Draw an X-axis parallel and down the plane and a Y-axis perpendicular to the plane and upward. (b) Find and draw the components of the forces on the X and Y-axes. (c) Find the acceleration of the block. Take g = 10 m/s2.
 13 Repeat Problem 12 for a coefficient of kinetic friction µk between the surface and the object of 0.154.
 14 The coefficient of kinetic friction between the block of mass m = 2.5 kg and the plane in Fig. 6 below is 1/6. Find (a) the acceleration of the block and (b) the tension in the string. Take g = 10 m/s2. 15 An object of mass m = 2 kg moves in a circle on a table with uniform circular motion. The speed of the object is 2 m/s and the radius of the circle is 0.5 m. Find the (a) frictional force acting on the object and (b) total force of the table on the object.
 16 A man of mass 60 kg pushes on a sled of mass 10 kg and the man and the sled accelerate forward with an acceleration of 2.0 m/s2. Neglect a frictional force on the sled and find (a) the force of the man on the sled, (b) the force of the sled on the man and (c) the frictional force of the snow on the man.
 17 A wooden rod of negligible mass is connected to the shaft of a motor. An object with mass m = 2 kg is attached to the other end of the rod. As the shaft rotates, the object moves in a vertical circle of radius 0.5 m with a constant speed of magnitude v = 3 m/s. (a) Find the magnitude of the centripetal acceleration for this object. The vertical circle path is shown in Fig. 7 below for an object that moves counter-clockwise. Redraw the figure and show on it, the direction of the velocity at (b) B, the bottom of the circle, (c) T, the top of the circle and (d) S, the side of the circle. Now draw the direction of the acceleration for (e) point B, (f) point T and (g) point S Find the force of the rod on the object For for (h) point B, (i) point T and (j) point S. 18 A 10-kg object rests on a scale in an elevator. Find the reading on the scale when the elevator moves with (a) a constant velocity of 5 m/s and (b) a constant acceleration of 5 m/s2 upward. Take g = 10 m/s2.
 19 A person of mass m stands on a bathroom scale in an elevator. Figure 8 below is a rough plot of scale reading as a function of time. Describe the motion of the elevator. 20 Two spheres of identical radii, one of lead, the other of wood fall from rest in air from a certain height. In this problem assume that the frictional force of the air is the same on both spheres. Will the spheres reach the ground at the same time?
 21 A block with a mass m = 2.0 kg initially at rest is pushed up the incline by a horizontal force F = 60 N (Fig. 9). The coefficient of kinetic friction between the block and the incline µk =1/2. Find the acceleration of the block. Homepage Sitemap
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