PH101 HW Force

# PH101 HW Force - This print-out should have 29 questions...

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Unformatted text preview: This print-out should have 29 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points No force is necessary to 1. stop an object from moving. 2. start an object moving. 3. keep an object moving the way it is al- ready moving. correct 4. cause a change in the motion of an ob- ject. Explanation: 002 10.0 points A push or pull that gives energy to an ob- ject, causing that object to start moving, stop moving, or change its motion is 1. pressure. 2. friction. 3. inertia. 4. a force. correct Explanation: 003 10.0 points Newton’s law of universal gravitation is F = G M m r 2 . Here, M and m are masses and r is the sep- aration distance. The dimension of force is specified by the equation F = ma . What are the SI units of the constant G ? 1. [ G ] = N m 2. [ G ] = W / m 3 3. [ G ] = m 3 / kg 2 / s 2 4. [ G ] = N m / s 2 5. [ G ] = kg / m 2 / s 2 6. [ G ] = J s / kg 7. [ G ] = m 2 / kg 2 / s 2 8. [ G ] = m / kg / s 2 9. [ G ] = m 3 / kg / s 2 correct 10. [ G ] = m 2 / kg Explanation: F = G M m r 2 so G = F r 2 M m . Dimensional analysis of G : kg m s 2 m 2 (kg) 2 = m 3 (kg s 2 ) . The common expression is [ G ] = m 3 / kg / s 2 . 004 (part 1 of 2) 10.0 points Sue and Jenny kick a soccer ball at exactly the same time. Sue’s foot exerts a force of 48 . 9 N to the north. Jenny’s foot exerts a force of 118 . 1 N to the east. a) What is the magnitude of the resultant force on the ball? Correct answer: 127 . 823 N. Explanation: f j F f s θ The magnitude of the resultant can be cal- culated using the Pythagorean Theorem: F = f 2 s + f 2 j = (48 . 9 N) 2 + (118 . 1 N) 2 = 127 . 823 N 005 (part 2 of 2) 10.0 points b) What is the direction of the resultant force (measured from East)? Correct answer: 22 . 4923 ◦ . Explanation: Jenny’s force is directed east, so f s is the side opposite θ and f j is the side adjacent, and tan θ = f s f j θ = arctan f s f j = arctan 48 . 9 N 118 . 1 N = 22 . 4923 ◦ 006 10.0 points Start a ball rolling down a bowling alley and you’ll find it moves slightly slower with time. Does this violate Newton’s law of inertia? Defend your answer. 1. None of these 2. No; air resistance and friction act upon the ball. correct 3. Yes; the air resistance cancels the friction and the total force on the ball is zero. 4. Yes; no force acts upon it. 5. No; the law of inertia can also be applied to moving objects. Explanation: If there were no force acting on the ball it would continue to move without slowing down. Air resistance along with slight fric- tion with the lane slows the ball down. This doesn’t violate the law of inertia because ex- ternal forces act on the ball....
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PH101 HW Force - This print-out should have 29 questions...

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