This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: fullwood (tf5349) Homework 5a Newtons Laws Catala (49033) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points What force pushes up on you when you jump vertically off the ground? 1. The force of air drag 2. The ground pushes up on you. correct 3. All are wrong. 4. The force of gravitation 5. Your feet push up on your body. Explanation: The only upward force is that of the grounds pushing up on you, in response to your pushing down on the ground. 002 10.0 points In order to slide a heavy desk across the floor at constant speed in a straight line, you have to exert a horizontal force of 300 Newtons. Compare the 300-Newton horizontal push- ing force F to the frictional force f between the desk and the ground. 1. F = f from Newtons third law. 2. F > f ; the frictional force is always less than any other force acting on the object. 3. F < f ; the frictional force is greater than the pushing force since it is such a heavy desk. 4. F = f from Newtons first law. correct 5. It depends on the direction the desk moves. Explanation: Since the desk moves at constant speed in a straight line, Newtons first law tells us the two forces must balance. 003 10.0 points An example of the weak nuclear force is 1. ocean tides. 2. nuclear decay. correct 3. static cling. 4. lightning. Explanation: 004 10.0 points An elevator is being lifted up an elevator shaft at a constant speed by a steel cable as shown in the figure below. All frictional effects are negligible. steel cable Elevator going up at constant speed In this situation, forces on the elevator are such that 1. the upward force by the cable is greater than the downward force of gravity. 2. the upward force by the cable is smaller than the downward force of gravity. 3. the upward force by the cable is equal to the downward force of gravity. correct 4. None of these. (The elevator goes up because the cable is being shortened, not be- cause an upward force is exerted on the eleva- tor by the cable.) 5. the upward force by the cable is greater than the sum of the downward force of gravity fullwood (tf5349) Homework 5a Newtons Laws Catala (49033) 2 and a downward force due to the air. Explanation: Since the elevator is being lifted at a con- stant speed, the net force on it is zero, there- fore, the upward force by the cable is equal to the downward force of gravity. 005 (part 1 of 4) 10.0 points Gravity on the surface of the moon is only 1 6 as strong as gravity on the Earth. What is the weight of a 21 kg object on the Earth? The acceleration of gravity is 10 m / s 2 . Correct answer: 210 N....
View Full Document