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Exam1Solution-EP1-S07

# Exam1Solution-EP1-S07 - Engineering Physics 1(Phys 213 Exam...

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9 3. (6 pts) A car travels on a straight road for 20 km at 40 km/h. It then continues in the same direction for another 20 km at 60 km/h. What is the average velocity of the car during the complete trip? (Assume that it moves in the positive x direction.) Δ t 1 = Δ x 1 /v 1 Δ t 1 = Δ x 1 /v 1 = (20 km)/(40 km/h) = 0.5 h = (20 km)/(60 km/h) = 0.333 h Since both displacements are in the same direction, Δ x = Δ x 1 + Δ x 2 = 20 km + 20 km = 40 km. The total time for the trip is Δ t = Δ t 1 + Δ t 2 = 0.833 h. Therefore the average velocity is v avg = Δ x/ Δ t = (40 km)/(0.833 h) = 48 km/h Answer________________ 4. The position of an object moving along an x axis is given by x = 2 t 3 - 4 t + 5 , where x is in meters and t is in seconds. a) (5 pts) What is the average velocity between 0 and 3 seconds? At t = 0 s, x 0 = 0 – 0 + 5 = 5 m At t = 3 s, x = 54 – 12 + 5 = 47 m v avg = Δ x/ Δ t = (47 – 5 m)/(3 s) = 14 m/s Answer________________ b) (5 pts) What is the average acceleration between 0 and 3 seconds? v ( t )= d x /d t = 6 t 2 – 4 At t = 0 v ( t )= -4 m/s. (this is initial velocity) At t = 3 s v ( t )= 50 m/s. (this is final velocity a avg = ( v v 0 )/ Δ t = (50 - (-4) m/s)/ 3 s = 18 m/s 2 Answer________________ c) (5 pts) At what time is the velocity zero? If there is more than one time, state each of the times?
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Exam1Solution-EP1-S07 - Engineering Physics 1(Phys 213 Exam...

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