exam1practiceSolutions

exam1practiceSolutions - Updated for 2007!!! 1. Convert all...

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Unformatted text preview: Updated for 2007!!! 1. Convert all of the following into proper mks units: (a) 2500 feet hr OK, we have two problems with the above expression, feet should be meters and hr should be seconds. We know that 1 foot = 12 inches, 1 inch = 2.45 cm, and 1 m = 100 cm. So: 2500 feet hr 12 inches 1 foot 2 . 54 cm 1 in 1 m 100 cm 1 hr 60 min 1 min 60 sec (1) 2500 12 2 . 54 100 60 60 m s (2) . 212 m s (3) (b) 3 miles 3 miles 5280 feet 1 mile 12 inches 1 foot 2 . 54 cm 1 in 1 m 100 cm (4) 3 5280 12 2 . 54 100 meters (5) 4828 meters (6) (c) 2 years 2 years 365 days 1 year 24 hours 1 day 60 minutes 1 hr 60 sec 1 min (7) 2 365 24 60 60 1 sec (8) 6 . 31 10 7 sec (9) (d) 12000 cm 3 12000 cm 3 1 m 100 cm 1 m 100 cm 1 m 100 cm (10) 12000 100 100 100 m 3 (11) . 012 m 3 (12) (e) 45 gram cm minute 2 1 45 gram cm minute 2 1 kg 1000 grams 1 m 100 cm 1 min 60 sec 1 min 60 sec (13) 45 1000 100 60 60 kg m s 2 (14) 1 . 25 10- 7 kg m s 2 (15) 1 . 25 10- 7 N (16) 2 2. You are driving along the road at 30 m s , when you notice a deer in the road 40 m in front of you. You immediately slam on the brakes and experience an acceleration of -10 m s 2 . (a) Where would you come to a stop if the deer were not in your way? ANSWER: Where is a question about position and is paraphrased as x=?. This is an ill-formed question. We must ask for x under a special condition (where you STOP ). Thus, the well-formed question is: x(v=0)=? To solve this, we call upon the x-v equation: v 2 = v 2 + 2 a ( x- x ) (17) 2 = 30 2 + 2(- 10)( x- 0) (18) 0 = 900- 20 x (19) x = 900 20 = 45 meters (20) You would hit the deer. (b) How fast are you going when you reach the deers position? ANSWER: The question how fast is answered by specifying a value for v. However, v=?, is an ill-formed question. We must instead ask: v(x=40)=? This is again solved using the x-v equation: v 2 = v 2 + 2 a ( x- x ) (21) v 2 = 30 2 + 2(- 10)(40- 0) (22) v 2 = 900- 800 (23) v 2 = 100 (24) v = 10 m s (25) (c) How long does it take you to get there? ANSWER: How long is a question about t (t=?). The well-formed variant of the question is: t(x=40)=? This is solved using the x-t relation: x = x + v t + 1 2 at 2 (26) 40 = 0 + 30 t + 1 2 (- 10) t 2 (27) 3 40 = 30 t- 5 t 2 (28) 5 t 2- 30 t + 40 = 0 (29) t =- b b 2- 4 ac 2 a (30) t = 30 30 2- 4 5 40 2 5 (31) t = 30 900- 800 10 (32) t = 30 100 10 (33) t = 30 10 10 (34) t = 3 1 (35) Since we clearly need the earliest time as the time you hit the deer, we get: t = 2 sec (36) Luckily this is one smart deer. The deer runs to the side and needs to move a minimum of 1.2 meters to avoid being hit. What acceleration of the deer is necessary to just avoid the collision with your car?...
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This note was uploaded on 06/12/2011 for the course PHY 131 taught by Professor Rijssenbeek during the Fall '03 term at SUNY Stony Brook.

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exam1practiceSolutions - Updated for 2007!!! 1. Convert all...

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