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PHY 2053, Spring 2009, Quiz 6 — Whiting 1. A mechanic pushes a 3.00 × 103 kg car from rest to a speed of v, doing 6,000 J of work in the process. During this time the car moves 25.0 m. Neglecting friction between the car and the road, find: a) v, and 1 W = mv 2 ⇒ 2 v= r 2W = m r 2 × 6000 = 2m/s. 3000 b) the horizontal force exerted on the car. W = F × d × cos(θ) ⇒ F = W 6000 = = 240 N, since θ = 0◦ . d × cos(θ) 25.0 2. An archer pulls her bowstring back 0.350 m by exerting a force that increases uniformly from zero to 245 N. a) What is the equivalent spring constant of the bow? Farcher = k × ∆x ⇒ k= 245 Farcher = = 700 N/m. ∆x 0.350 b) How much work does the archer do in pulling the bow? W = 1 1 Farcher × ∆x = k × (∆x)2 = 0.500 × 245 × 0.350 = 42.875 J. 2 2