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Unformatted text preview: Problem 3.32 To get to a concert in time, a harpsichordist has to drive 122 mi in 2.00 h. (a) If he drove at an average speed of 55.0 mi/h in a due west direction for the first 1.20 h, what must be his average speed if he is heading 30.0 south of west for the remaining 48.0 min? (b) What is his average velocity for the entire trip? What do we want to know in a? the speed a) speed we dont care about the direction, would it be west, north west east to solve a!!!! What do we know, the total length of the trip, we know can calculate the length already gone through having the velocity and the time and from there the length still to go though and the Time left, so the average speed of the remaining part And the time left so we can can calculate the average speed of the remaining part If he drove at an average speed of 55.0 m/h for 1.2h, he drove 55.0m/hx1.20h= 66.0 miles out of The 122 miles, the distance left to drive is 122-66.0 = 56.0 miles and the time left is 2.00h-1.20h=0.80 h so the average speed in that remaining part of the trip should be 56/0.80=70m/h What do we want to know the average velocity ? b) velocity , we do care about directions !!!!! The average velocity for the entire trip, is the total displacement divided by the 2 hours, Namely r/2hours r=v( x 2 + y 2 ) x = 55.0m/h*1.20 h + 56(cos30)=114.5 mi y = 56sin(30) = 28 mi v= r/ t=v(114.6 2 +28 2 ) / 2.00 = 59mi/h = tan-1 (28/114.5) = 14 deg South of West 30deg S W r N Problem 3.23. Vector has magnitude 7.1 and direction 14 below the + x- axis. Vector has x-component C x = 1.8 and y component C y = 6.7. Compute (a) the x- and y components of ; (b) the magnitude and direction of ; (c) the magnitude and direction of + ; (d) the magnitude and direction of...
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- Spring '09