Physics- Chapter 4

What is the mass of a 495-N weight? ______ kg

50.48

A 44-kg woman in an elevator is accelerating upward at a rate of 1.1 m/s2. (a) What is the net force acting upon the woman? _____ N (b) What is the gravitational force acting upon the woman? _____ N (c) What is the normal force pushing upward on the woman's feet? _____ N

(a) 48.4 (b) 431.2 (c) 479.6

A ball hangs from a string attached to the ceiling, as shown in the diagram. (a) What forces act on the ball? (Select all that apply.) a. tension from the string b. normal force c. coulomb force d. force due to gravitation (b) What is the net force acting on the ball? Explain. a. The net force on the ball is the force due to gravitation b. The net force equals zero because the ball is not accelerating in any direction. c. The net force is the sum of the magnitudes of the tension in the string and the force due to gravitation. d. The net force on the ball is the force due to the tension in the string. (c) Which of the following forces related to those identified in part (a) is a reaction force described by Newton's third law of motion? (Select all that apply.) a. normal force of ball on ceiling b. force of ball on string c. ball's gravitational force on earth d. coulomb force of ball on earth

(a) a. tension from the string d. force due to gravitation (b) b. The net force equals zero because the ball is not accelerating in any direction. (c) b. force of ball on string c. ball's gravitational force on earth

Two blocks with the same mass are connected by a string and are pulled across a frictionless surface by a constant force, F, exerted by a string (see diagram). (a) Will the two blocks move with constant velocity? Explain. a. Yes, the applied force is constant and implies a zero acceleration that results in a constant velocity. b. No, the applied force is constant and implies a constant acceleration that results in constantly increasing velocity. c. Whether the velocity is constant cannot be determined without knowing the magnitude of the force. (b) Will the tension in the connecting string be greater than, less than, or equal to the force F? Explain. a. The tension in the connecting string will be greater than F. While both bodies have the same acceleration, the force F accelerates a total mass, 2m, and the force in the connecting string accelerates a mass, m, so it is twice F. b. The tension in the connecting string will be less than F. While both bodies have the same acceleration, the force F accelerates a total mass, 2m, and the force in the connecting string accelerates a mass, m, so it is half of F. c. The tension in the connecting string will be equal to F. Since both bodies have the same acceleration, the force F that accelerates the first mass and the force in the connecting string that accelerates the second mass must be equal.

(a) b. No, the applied force is constant and implies a constant acceleration that results in constantly increasing velocity. (b) b. The tension in the connecting string will be less than F. While both bodies have the same acceleration, the force F accelerates a total mass, 2m, and the force in the connecting string accelerates a mass, m, so it is half of F.

A car goes around a curve traveling at constant speed. (a) Is the acceleration of the car zero in this process? Explain. a. Yes, the acceleration is zero because the speed of the car is constant. b. Yes, but only if the road is banked so that the car can maintain a constant speed around the curve. c. No, the velocity of the car is continuously changing direction while on the curve so there is acceleration. (b) Is there a non-zero net force acting on the car in this case? Explain. a. Yes, a non-zero net force is required to produce an acceleration. b. Yes, a non-zero net force is required for the car to maintain a constant speed with no acceleration as it goes around the curve. c. No, the car is not accelerating so the net force is equal to zero.

(a) c. No, the velocity of the car is continuously changing direction while on the curve so there is acceleration. (b) a. Yes, a non-zero net force is required to produce an acceleration.

Two identical cans, one filled with lead shot and the other with feathers, are dropped from the same height by a student standing on a chair. (a) Which can, if either, experiences the greater force due to the gravitational attraction of the Earth? a. Both cans experience the same force due to gravity because the force due to gravity is the same for all objects. b. The feather-filled can experiences a greater force due to gravity since the effect of air resistance is reduced by putting the feathers in the can. c. The lead shot-filled can experiences a greater force due to gravity because it contains more mass. (b) Which can, if either, experiences the greater acceleration due to gravity? Explain. a. The lead shot-filled can experiences a greater acceleration due to gravity because of its greater mass. b. Both cans experience the same acceleleration due to gravity regardless of mass. c. The feather-filled can experiences a greater acceleration due to gravity since air resistance is reduced by putting the feathers in the can.

(a) c. The lead shot-filled can experiences a greater force due to gravity because it contains more mass. (b) b. Both cans experience the same acceleleration due to gravity regardless of mass.

A 3.0-kg block being pulled across a table by a horizontal force of 50 N also experiences a frictional force of 10 N. What is the acceleration of the block? _____ m/s2

13.3

A single force of 35 N acts upon a 15-kg block. What is the magnitude of the acceleration of the block? _____ m/s2

2.3

A net force of 36 N acting on a wooden block produces an acceleration of 1.3 m/s2 for the block. What is the mass of the block? ____ kg

27.7

What is the weight of a 30-kg mass? _____ N

294.2

A heavy ball with a mass of 3.0 kg is observed to accelerate at a rate of 3.0 m/s2. What is the size of the net force acting on this ball? _____ N

9

An object moving horizontally across a table is observed to slow down. Is there a non-zero net force acting on the object? Explain. a. Yes, there must be a net force directed opposite the motion to produce the observed negative acceleration. b. Yes, there must be a net force in the same direction of the motion to produce the observed negative acceleration. c. No, the force acting on the object must be equal to zero so that it will slow down. d. No, a non-zero net force cannot exist due to conservation of energy.

a. Yes, there must be a net force directed opposite the motion to produce the observed negative acceleration.

Two bodies have quite different masses, but the net force applied to each of them is the same. The acceleration of: a. the more massive body is larger. b. the less massive body is larger. c. each body is the same.

b. the less massive body is larger.

An elevator of mass 500 kg is caused to accelerate upward at 4.0 m/s2 by a force in the cable. What is the force exerted by the cable? a. 4,900 N b. 2,900 N c. 6,900 N d. 2,000 N e. zero

c. 6,900 N

If you get into an elevator on the top floor of a large building and the elevator begins to accelerate downward, will the normal force pushing up on your feet be greater than, equal to, or less than the force of gravity pulling downward on you? Explain. a. The normal force will be greater than your true weight because the normal force will now equal your true weight plus the descending force. b. The normal force will be equal to your true weight because the normal force acts equal and opposite only to the force due to gravitation. c. The normal force will be less than your true weight because the normal force will now equal your true weight plus the descending force.

c. The normal force will be less than your true weight because the normal force will now equal your true weight plus the descending force.

The frictional force, due to air resistance, acting on an object is always: a. in the upward direction. b. smaller than object's weight c. in the opposite direction to the objects motion. d. in the direction of the objects motion. e. greater than the net force.

c. in the opposite direction to the objects motion.

A 100 pound sack of potatoes falls from an airplane. As the velocity of the falling sack increases, so does the air resistance on it. When the air resistance equals 100 pounds, the acceleration of the sack will be: a. 9.8 m/s2. b. 9.8 m/s. c. zero. d. infinite.

c. zero.

The acceleration of gravity on the moon's surface is about 1/6 of that on the Earth's surface. An object on the Earth is to be taken to the Moon. We can state that, compared to the Earth, a. the object's weight will be the same on the Moon. b. the object's mass will be greater on the Moon. c. the object's mass will be less on the Moon. d. the object's weight will be greater on the Moon. e. the object's mass will be the same on the Moon.

e. the object's mass will be the same on the Moon.