PHY302K-Sai-HW6-solutions

# PHY302K-Sai-HW6-solutions - Oslund(hno56 Homework 6...

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Oslund (hno56) – Homework 6 – sai – (58015) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 (part 1 oF 2) 10.0 points Two blocks, A and B , are connected by a compressed spring. The mass oF block A is twice that oF block B . Immediately aFter release, compare the net Force on block A to the net Force on block B . The table is Frictionless and the mass oF the spring is zero. 1. F A,net and F A,net are both directed toward the leFt with F A,net larger than F A,net , but not twice as large. Block A is pulling block B . 2. F A,net is equal in magnitude and opposite in direction to F B,net , and not zero. correct 3. F A,net will be in the opposite direction and halF as large as F B,net . 4. There is no net Force on block A or block B . 5. F A,net is equal in magnitude and direction to F B,net , and not zero. 6. F B,net will be in the opposite direction and halF as large as F A,net . Explanation: F A,net is the Force on block A From the spring, it’s reaction Force is the Force acting on the spring by block A , which we denote as F S,A . They have the same magnitude but they are in opposite directions. Similarly, F B,net has a reaction Force F S,B . The total Force on the spring ± F S,net = ± F S,A + ± F S,B = - ± F A,net - ± F B,net = - ± ± F A,net + ± F B,net ² = m spring · a =0 · a . So that ± F A,net and ± F B,net must have the same magnitude but in opposite directions. Note: This is correct only when the mass oF the spring can be neglected as mentioned in the problem. 002 (part 2 oF 2) 10.0 points Which oF the Following best describes the sit- uation aFter the blocks are released? 1. The total momentum oF the system oF blocks is conserved because there is no net external Force. correct 2. The total momentum oF the system oF blocks is not conserved because there is an external velocity acting on the system. 3. The total momentum oF the system is not conserved because there are external Forces; e.g. , gravity. 4. Momentum For any body is always con- served. 5. The momentum oF block A is conserved and the momentum oF block B is conserved. However, the total momentum oF the system oF blocks is not conserved. 6. The momentum oF block A is conserved and the momentum oF block B is conserved. It Follows that the total momentum oF the system oF blocks is also conserved. Explanation: Neither block A nor B conserves its mo- mentum since there is a Force on each oF them. However, once we consider the two blocks and the spring as a whole system, its momentum is conserved since there is no external Force. The contribution oF momentum From the spring is zero since its mass is zero. 003 10.0 points A 62.8 kg astronaut is on a space walk when the tether line to the shuttle breaks. The astronaut is able to throw a 11.0 kg oxygen tank in a direction away From the shuttle with a speed oF 13.7 m/s, propelling the astronaut back to the shuttle.

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Oslund (hno56) – Homework 6 – sai – (58015) 2 Assuming that the astronaut starts from rest, Fnd the Fnal speed of the astronaut after throwing the tank.
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PHY302K-Sai-HW6-solutions - Oslund(hno56 Homework 6...

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