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final_spr06_SOLN

# final_spr06_SOLN - 9May06 LeClair Name PH 105(Practice...

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Unformatted text preview: 9May06 LeClair Name: PH 105 (Practice) Final Exam This is the final from last semester, which you can use as a practice test. Part 1: Multiple choice (65%) Answer all questions. 1. Stephans law relating the (thermal) radiation power to the temperature of the radiating body is expressed as: P = AT 4 , where P is power in Watts (W), T is temperature in Kelvins, and A is an area in m 2 . What are the units of ? N W/ ( m 2 K 4 ) W/K 4 W m 2 /K 4 K 4 / ( W m 2 ) Write the equation out, then plug in the units you know. P = AT 4 [ W ] = m 2 K 4 Now solve for , and we are done: = [ W ] [ m 2 ] [ K 4 ] 2. A particles velocity is given by: v ( t ) = mg b 1- e- ( b m ) t where b is a constant (units of kg/sec ), and the particles mass is m . Find the acceleration at t = 0. gb/m 2 g/b N g g/b Recall that a = d v d t 1 a ( t ) = d v d t = mg b b m e- ( b m ) t = ge- ( b m ) t a (0) = ge- ( b m ) = g (As it turns out, this is the velocity versus time for a falling particle if we include a resistive force ( e.g., air drag) proportional to velocity, ~ F drag =- b ~ v .) 3. A projectile is launched at an initial angle of 75 over level ground, and lands at a distance d away. Neglecting air resistance, at what other launch angle ( &amp;lt; 90 ) would the projectile have landed at the same distance d ? 5 35 25 N 15 If you recall the formula for the range of a particle, this is easier. R = v 2 i sin (2 ) g The sin (2 ) dependence of R means that if some angle 45 + works, then 45 - must also work. So, if 75 works, so must 15 Alternatively, one can easily derive the range formula given the generic x ( t ) and y ( t ) forms. 4. A projectile is launched at an initial angle of over level ground, and at the same time, a second projectile is dropped from a height h a distance x away from the launch site. Neglecting air resistance, what is the required height h for a given x and such that the two projectiles collide? 2 not enough information h = x/ tan N h = x tan h = x sin See example 4.4 in the text. 5. In which of the pictures below does the scale read the largest value? a N b a and b are the same, and both more than c c In all cases, the scale measures the tension in the string. In case a, this is only 5 kg, the tension for each string on either side of the scale is the same. It would be the same if, instead of connecting the right side weight, we connected that string to the wall. In case c, the tension in the string is only one component of the objects weight, less than 5 kg. In case b, however, both weights contribute to the tension in the string, 10 kg....
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final_spr06_SOLN - 9May06 LeClair Name PH 105(Practice...

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