Physics 1: exam 2 Questions & Answers

Physics 1: exam 2 Questions & Answers *Mark each of the following statements as true or false*. If a statement refers to "two objects" interacting via some force, you are not to assume that these two objects have the same mass. 1.) Every force has one and only one 3rd law pair force. 2.) The two forces in each pair act in opposite directions. 3.) The two forces in each pair can act on the same object or on different objects. 4.) The two forces in each pair may have different physical origins (for instance, one of the forces could be due to gravity, and its pair force could be a normal contact force). 5.) The two forces of a 3rd law pair always act on different objects. 6.) Given that two objects interact via some force, the accelerations of these two objects have the same magnitude but opposite directions. (Assume no other forces act on either object.) - ANSWER: 1.) True 2.) True 3.) False 4.) False 5.) True 6.) False *period, T* of the motion is - ANSWER: the time it takes to travel once around a circle. -Since the distance traveled around the circle is 2πr, the speed of an object in uniform circular motion is: V = 2πr / T -period = time it takes to go around one full circle -if change in distance = V x T and the distance traveled is the circumference of the circle, then 2πr = V x T --> V = 2πr / T 1 Newton of force is the force needed to give an acceleration of - ANSWER: 1 m/s^2 to an object of 1 kilogram. [N] = [kg m/s2] 1.) An object is moving with constant velocity. Which of the following statements is true? A) There are no forces acting on the object. B) There is no frictional force acting on the object. C) A constant force is being applied in the direction of motion. D) A constant force is being applied in the direction opposite of motion. E) The net force on the object is zero. - ANSWER: E.) The net force on the object is zero. -no acceleration 10.) A 40.0-kg crate is being raised by means of a rope. Its upward acceleration is 2.00 m/s2. What is the force exerted by the rope on the crate? - ANSWER: *A* 472 N force = tension W = 40 x 9.8 F = ma T-W T = ma + W 11.) A 40.0-kg suitcase is being pulled along the ground by means of a strap which exerts a force of 10.0 N at an angle of 43.0° above the horizontal. What is the normal force exerted by the ground? - ANSWER: Fy = 10sin40 --> Fy = 6.43 Fy and N are upward forces weight is a downward force so.... N + Fy = W W = mg --> W = 392 N = 392 - 6.43 --> *N = 385* *B* 12.) T/F: The force of static friction between two surfaces is independent of the area of contact between the surfaces. - ANSWER: *True* -fs = μsN -N = weight with no other forces present 13.) A packing crate slides down an inclined ramp at constant velocity. Thus we can deduce that - ANSWER: -no net upward force -no downward force (no acceleration) -friction force acting