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oldhw 09 - alexander(jra2623 oldhomework 09 Turner(92510...

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alexander (jra2623) – oldhomework 09 – Turner – (92510) 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points What is the net force on a 1-N apple when you hold it at rest above your head and what is the net force on it after you release it? 1. 1 N, 0 N 2. All are wrong. 3. 0 N, 0 N 4. 0 N, 1 N correct 5. 1 N, 1 N Explanation: When held at rest the upward support force equals the gravitational force on the apple and the net force is zero. When released, the upward support force is no longer there and the net force is gravitational force, 1 N. (If the apple falls fast enough for air resistance to be important, then the net force will be less than 1 N, and eventually can reach zero if air resistance builds up to 1 N.) 002 (part 1 of 5) 10.0 points Three blocks are in contact with each other on a frictionless horizontal surface. A 543 N horizontal force is applied to the block with mass of 2 . 3 kg as shown in the figure below. The acceleration of gravity is 9 . 8 m / s 2 . 2 . 3 kg 4 . 8 kg 7 . 3 kg F a) What is the net force on the block with mass 2 . 3 kg? Correct answer: 86 . 7292 N. Explanation: m 1 m 2 m 3 F Given : F = 543 N , m 1 = 2 . 3 kg , m 2 = 4 . 8 kg , m 3 = 7 . 3 kg , and g = 9 . 8 m / s 2 . Basic Concepts: F net = m a m total = m 1 + m 2 + m 3 Solution: m 1 + m 2 + m 3 N g F ( m 1 + m 2 + m 3 ) g F = ( m 1 + m 2 + m 3 ) a . The acceleration of the system is a = F m 1 + m 2 + m 3 = 543 N 2 . 3 kg + 4 . 8 kg + 7 . 3 kg = 37 . 7083 m / s 2 to the right.
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