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Pop Quiz

Pop Quiz. 1. A car travels one-half of a 1-km trip at a constant speed of 10.0 km/hr. It then travels the other half of the trip at twice the speed (20.0 km/hr). What is the average speed for the whole 1-km trip? (A) 10.0 km/hr (B) 13.3 km/hr (C) 16.6 km/hr (D) 15 km/hr (E) 18 km/hr

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Pop Quiz

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  1. Pop Quiz 1. A car travels one-half of a 1-km trip at a constant speed of 10.0 km/hr. It then travels the other half of the trip at twice the speed (20.0 km/hr). What is the average speed for the whole 1-km trip? (A) 10.0 km/hr (B) 13.3 km/hr (C) 16.6 km/hr (D) 15 km/hr (E) 18 km/hr 2. How long will it take a car, starting from rest and accelerating uniformly in a straight line at 5 m/s2, to cover a distance of 200 m? (A) 9.0 s; (B) 10.5 s; (C) 12.0 s; (D) 15.5 s; (E) 20.0 s.

  2. x D E F C B A t Pop Quiz 3. Here is a position-versus-time graph. Describe in words the motion of the object and sketch the corresponding velocity-versus-time graph.

  3. Vectors: addition and subtraction • Any vector arrow can be drawn to scale on a graphic paper in a specified direction. The vector arrow has a head and a tail. • Addition of two or more vectors involves drawing the tail of the second vector right at the head of the first (“The tail-to-head method), and so on, the sum of all the vectors (“the resultant vector”) is the one vector arrow pointing from the tail of the first vector to the head of the last vector.

  4. Vectors: addition and subtraction • A+B = B+A, so it does not matter which one vector to start with; • Vector -A always has the same magnitude but opposite in direction of vector A: B-A = B+(-A) • Vector A can be manipulated by a scalar factor, only changing its magnitude not the direction. Exercise: given vector A , sketch 2A, -1/2A A

  5. Vector Components • Any vector A can be split into two components, one pointing in the x-direction and one in the y-direction. These components form two sides of a right triangle having a hypotenuse with the same magnitude as A: Ax = Acosθ Ay = Asinθ • The magnitude and direction of vector A are related to its component: |A| = Ax2 + Ay2 tan θ = Ay /Ax

  6. Vector Components • If vector R is the sum of vectors A and B, then Rx = Ax + Bx and Ry =Ay + By Exercise: A roller coaster moves 200 ft horizontally and then rises 135 feet at an angle of 30.0o above the horizontal. It then travels 135 feet at an angle of 40.0o below the horizontal. Use graphical technique to estimate the roller coaster’s displacement from its starting point, then use vector components to calculate the exact displacement.

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