Physics1A_Nathan_Winter13_Midterm1.pdf

# Note that a fraction of the graded exams will be

• Test Prep
• DarkThunderKnight27
• 6

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negate your chances for a regrade. Note that a fraction of the graded exams will be photocopied prior to returning them to you. 1 24 2 38 3 38 Total 100 Useful constants: g = 9 . 8 m / s 2

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1. (24 pts) Starting from her house, Debbie walks her bike 80 m east at a constant speed of 2 m/s. Wasting no time, she then immediately climbs onto her bike and rides it at a constant speed of 12 m/s for 300 m along a path directed 60 deg south of east. For this entire trip, what are Debbie’s (i) average speed and (ii) average velocity? Define the positive x -direction as east and the positive y -direction as north. We first compute the total time required for Debbie’s trip: Δ t = Δ t 1 + Δ t 2 = L 1 v 1 + L 2 v 2 = 80 2 + 300 12 = 65 s Debbie’s average speed is her total distance over time: ¯ v speed = L 1 + L 2 Δ t = 80 + 300 65 = 5 . 85 m / s Debbie’s average velocity is her change in displacement over time: v ave , x = Δ x Δ t = L 1 + L 2 cos Δ t = 80 + (300) cos(60) 65 = 3 . 54 m / s v ave , y = Δ y Δ t = - L 2 sin Δ t = - (300) sin(60) 65 = - 4 . 00 m / s 2
2. (38 pts) Inside an elevator which is initially at rest, you kick a soccer ball which leaves the floor at 6 m/s directed upward and to the right at 40 deg above the horizontal. (a) What maximum height does the soccer ball reach above the stationary elevator floor? (b) At the instant the soccer ball reaches its maximum height, the elevator begins to accelerate upward from rest at a constant rate of 5 m/s 2 . What total horizontal distance does the ball travel from where it was kicked to where it returns to the elevator floor?

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• Spring '14
• Velocity, Sin, Debbie, MCR, mcr g sin

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