physics exam 2

A block of mass 2kg is acted upon by two forces: 3N (directed to the left) and 4N (directed to the right). What can you say about the block's motion? It must be moving to the left. It must be moving to the right. It must be at rest. It could be moving to the left, moving to the right, or be instantaneously at rest.

It could be moving to the left, moving to the right, or be instantaneously at rest. The acceleration of an object tells you nothing about its velocity--the direction and speed at which it is moving. In this case, the net force on (and therefore the acceleration of) the block is to the right, but the block could be moving left, right, or in any other direction.

Two forces, of magnitude 4Nand 10N, are applied to an object. The relative direction of the forces is unknown. The net force acting on the object __________. cannot have a magnitude equal to 5N cannot have a magnitude equal to 10N cannot have the same direction as the force with magnitude 10N must have a magnitude greater than 10N

cannot have a magnitude equal to 5N

An object is moving with constant velocity. Which of the following best describes the force(s) acting on the object? An object is moving with constant velocity. No forces are acting on the object. A constant net force is acting on the object in a direction opposite of the motion. A constant net force is acting on the object in a direction perpendicular to the direction of motion. A constant net force is acting on the object in the direction of the motion.

An object is moving with constant velocity. No forces are acting on the object. Because f=m*a a depends on change in velocity. but since velocity is constant acceleration is 0 and anything times 0=0

An object cannot remain at rest unless which of the following holds? The net force acting on it is zero. The net force acting on it is constant and nonzero. There are no forces at all acting on it. There is only one force acting on it.

Answer-The net force acting on it is zero. If there is a net force acting on a body, regardless of whether it is a constant force, the body accelerates. If the body is at rest and the net force acting on it is zero, then it will remain at rest. The net force could be zero either because there are no forces acting on the body at all or because several forces are acting on the body but they all cancel out.

An astronaut is taking a space walk near the shuttle when her safety tether breaks. What should the astronaut do to get back to the shuttle? Attempt to "swim" toward the shuttle. Take slow steps toward the shuttle. Take a tool from her tool belt and throw it away from the shuttle. Take the portion of the safety tether still attached to her belt and throw it toward the shuttle.

Take a tool from her tool belt and throw it away from the shuttle. As the astronaut throws the tool away from the shuttle, she exerts a force in the direction away from the shuttle. Then, by Newton's 3rd law, the tool will exert an opposite force on her. Thus, as she throws the tool, a force directed toward the shuttle will act on the astronaut. Newton's 2nd law stipulates that the astronaut would acquire an acceleration toward the shuttle.

Two objects attract each other gravitationally. If the distance between their centers decreases by a factor of 2, how does the gravitational force between them change? The gravitational force increases by a factor of 2. The gravitational force increases by a factor of 4. The gravitational force decreases by a factor of 4. The gravitational force decreases by a factor of 2. The gravitational force remains unchanged.

The gravitational force increases by a factor of 4.

If a block is moving to the left at a constant velocity, what can one conclude? There is exactly one force applied to the block. The net force applied to the block is directed to the left. The net force applied to the block is zero. There must be no forces at all applied to the block.

The net force applied to the block is zero. If there is a net force acting on a body, regardless of whether the body is already moving, the body accelerates. If a body is moving with constant velocity, then it is not accelerating and the net force acting on it is zero. The net force could be zero either because there are no forces acting on the body at all or because several forces are acting on the body but they all cancel out.

A constant net force acts on an object. Which of the following best describes the object's motion? The object is moving with a constant acceleration. The object is moving with a decreasing acceleration. The object is moving with a constant velocity. The object is moving with an increasing acceleration. The object is at rest; its position is constant.

The object is moving with a constant acceleration. newtons 2nd law. f=ma

Assuming that the astronaut can throw any tool with the same force, what tool should be thrown to get back to the shuttle as quickly as possible? You should consider how much mass is left behind as the object is thrown as well as the mass of the object itself. The tool with the smallest mass. The tool with the largest mass. Any tool, since the mass of the tool would make no difference

The tool with the largest mass. The force that acts on the astronaut must equal in magnitude the force that she exerts on the tool. Therefore, if she exerts the same force on any tool, the force acting on her will be independent of the mass of the tool. However, the acceleration that the astronaut would acquire is inversely proportional to her mass since she is acted upon by a constant force. If she throws the tool with the largest mass, the remaining mass (the astronaut plus her remaining tools) would be smallest—and the acceleration the greatest!

If the astronaut throws the tool with a force of 16.0 N, what is the magnitude of the acceleration a of the astronaut during the throw? Assume that the total mass of the astronaut after she throws the tool is 80.0 kg. Express your answer in meters per second squared.

a= 0.200 m/s^2 F=ma F/m=a 16N/80 kg = a

A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be __________. continuously changing direction moving at constant velocity moving with a constant nonzero acceleration moving with continuously increasing acceleration

moving with a constant nonzero acceleration Since there is a net force acting, the body does not move at a constant velocity, but it accelerates instead. However, the force acting on the body is constant. Hence, according to Newton's 2nd law of motion, the acceleration of the body is also constant.