Solution 2

# Solution 2 - yang(ey942 HW02 TSOI(58160 This print-out...

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yang (ey942) – HW02 – TSOI – (58160) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points The velocity oF a projectile at launch has a horizontal component v h and a vertical com- ponent v v . Note: Air resistance is negligible. When the projectile is at the highest point oF its trajectory, which oF the Following show the vertical and the horizontal components oF its velocity and the vertical component oF its acceleration in 3 columns? Vertical Horizontal Vertical Velocity Velocity Acceleration 1. 0 0 g 2. 0 v h 0 3. v v 0 0 4. v v v h 0 5. 0 v h g correct Explanation: Basic concept: Newton’s second law oF mo- tion V F = mVa The only Force on the projectile is the gravita- tional Force, which gives projectile a constant vertical acceleration oF the magnitude g . There is no acceleration in the horizontal direction, which means at the highest point, the horizontal component oF the velocity is the same as the initial value v h . One other obvious thing: the vertical com- ponent oF the velocity is zero at the highest point, because From the trajectory, the projec- tile moves horizontally at the highest point. 002 (part 1 oF 2) 10.0 points A camel sets out to cross the desert, which is 44 . 8 km wide in the north-south direc- tion. The camel walks at the uniForm speed 4 . 29 km / hr along a straight line in the direc- tion 48 . 4 north oF East (only the camel knows why he chose that particular direction). θ W E N S How long will it take the camel to cross the desert? Correct answer: 13 . 9648 hr. Explanation: Let the total distance walked by the camel be L ; then the camel’s northward displace- ment is L N = L sin θ while his eastward displacement is L E = L cos θ . To cross the desert, the camel needs L N = desert width = 44 . 8 km and hence L = L E sin θ = 44 . 8 km sin 48 . 4 = 59 . 9092 km , and the time he needs to walk this distance is simply T = L v = 59 . 9092 km 4 . 29 km / hr = 13 . 9648 hr . 003 (part 2 oF 2) 10.0 points Calculate the camel’s eastward displacement while he crosses the desert. Correct answer: 39 . 7753 km. Explanation: As we already mentioned, L E = L cos θ = (59 . 9092 km) cos(48 . 4 ) = 39 . 7753 km . 004 (part 1 oF 3) 10.0 points Consider the setup oF a gun aimed at a target (such as a monkey) as shown in the fgure. The target is to be dropped From the point A at t = 0, the same moment as the gun is fred.

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yang (ey942) – HW02 – TSOI – (58160) 2 The bullet hits the target at a point P, which is at the same horizontal level as the gun. Let the initial speed of the bullet be v 0 , let the angle between the vector Vv 0 and the horizontal ( x -) direction be θ , and OP = L and AP = h . The gravitational acceleration is g . Denote the time taken to hit the target by T .
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Solution 2 - yang(ey942 HW02 TSOI(58160 This print-out...

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