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# SOL25 - Thevalingam Donald Homework 25 Due Apr 3 2007...

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Thevalingam, Donald – Homework 25 – Due: Apr 3 2007, midnight – Inst: Eslami 1 This print-out should have 10 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 force of 2080 N is needed to bring a car moving at 25 . 2 m / s to a halt in 18 . 3 s. What is the mass of the car? Correct answer: 1510 . 48 kg. Explanation: Basic Concepts: Impulse-momentum re- lationship m Δ v = F Δ t . Solution: The car is brought to a halt, so Δ v = 0 - v = - v The force is negative, so m ( - v ) = ( - F ) t m = - F t - v = F t v . keywords: 002 (part 1 of 1) 10 points Small rockets are used to make small adjust- ments in the speed of satellites. One such rocket has a thrust of 46 N. If it is fired to change the velocity of a(n) 82000 kg space craft by 66 cm / s, how long should it be fired? Correct answer: 1176 . 52 s. Explanation: Impulse is defined by I = F t = m Δ v so t = m Δ v F Dimensional analysis: for t kg · cm / s N · 1 m 100 cm = kg · m / s kg · m / s 2 = s keywords: 003 (part 1 of 2) 10 points A revolutionary war cannon, with a mass of 2120 kg, fires a 22 . 5 kg ball horizontally. The cannonball has a speed of 116 m / s after it has left the barrel. The cannon carriage is on a flat platform and is free to roll horizontally. What is the speed of the cannon immedi- ately after it was fired? Correct answer: 1 . 23113 m / s. Explanation: Let : m = 22 . 5 kg , M = 2120 kg , and v = 116 m / s . The cannon’s velocity immediately after it was fired is found by using conservation of momentum along the horizontal direction: M V + m v = 0 ⇒ - V = m M v where M

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SOL25 - Thevalingam Donald Homework 25 Due Apr 3 2007...

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