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Unformatted text preview: Bautista, Aldo – Midterm 1 – Due: Sep 21 2005, 11:00 pm – Inst: Maxim Tsoi 1 This print-out should have 17 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points A ball is thrown upward. After reaching a maximum height, it continues falling back to- wards Earth. On the way down, the ball is caught at the same height at which it was thrown upward. Neglect: Air resistance. The acceleration of gravity is 9 . 8 m / s 2 . Its initial vertical speed v , acceleration of gravity g , and maximum height h max are shown in the figure below. v 9 . 8m / s 2 h max If the time ( up and down ) the ball remains in the air is t trip , calculate its speed v f when it caught. 1. v f = g t trip 2. v f = 1 4 g t trip 3. v f = √ 2 3 g t trip 4. v f = 1 2 g t trip correct 5. v f = 1 √ 2 g t trip 6. v f = 4 g t trip 7. v f = 2 3 g t trip 8. v f = 1 3 g t trip 9. v f = √ 2 g t trip 10. v f = 2 g t trip Explanation: Basic Concept: For constant accelera- tion, we have v = g t (1) y = y + v t + 1 2 at 2 . (2) Solution: The velocity at the top is zero. Since we know velocities and acceleration, Eq. 1 containing h max = y- y , a , and t. Choose the positive direction to be up, then a =- g and t up = v g . From symmetry, t down = t up , we have t trip = 2 v g , or v f = v = 1 2 g t trip . 002 (part 1 of 1) 10 points A jet airliner moving initially at 444 mph to the east where there is no wind moves into a region where the wind is blowing at 196 mph in a direction 59 ◦ north of east. What is the new speed of the aircraft with respect to the ground? Correct answer: 570 . 257 mph. Explanation: V jet V wind V φ θ The new velocity of the aircraft is the sum of the initial velocity and the velocity of the wind: ~v f = ~v i + ~v wind = v x ˆ ı + v y ˆ Bautista, Aldo – Midterm 1 – Due: Sep 21 2005, 11:00 pm – Inst: Maxim Tsoi 2 where v x = v i + v wind cos φ v y = v wind sin φ with φ being the angle between v wind and v jet . So the speed is | ~v | = q v 2 x + v 2 y . 003 (part 1 of 1) 10 points A solid aluminum cube has sides each of length L. A second cube of the same ma- terial has sides four times the length of the first cube, i.e. , 4 L. Compared to the first cube, the total sur- face area of the second cube is 1. twenty-seven times as much as the first cube. 2. sixteen times as much as the first cube. correct 3. twenty-four times as much as the first cube. 4. ninty-six times as much as the first cube. 5. nine times as much as the first cube. 6. two times as much as the first cube. 7. four times as much as the first cube. 8. None of these 9. sixty-four times as much as the first cube....
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This note was uploaded on 10/13/2009 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas.
- Fall '08