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# solution24 - fullwood(tf5349 – Homework 5a Newton’s...

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Unformatted text preview: fullwood (tf5349) – Homework 5a Newton’s 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 ground’s 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 Newton’s 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 Newton’s first law. correct 5. It depends on the direction the desk moves. Explanation: Since the desk moves at constant speed in a straight line, Newton’s 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 Newton’s 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....
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## This note was uploaded on 06/10/2010 for the course PHY 100 taught by Professor Pro.kiroshima during the Spring '10 term at Adelphi.

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solution24 - fullwood(tf5349 – Homework 5a Newton’s...

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