# Chap6 - 2 Strategy The distance is equal to the speed times...

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2. Strategy The distance is equal to the speed times the time interval. Use Eq. (6-1). Solution Find the work done by the rope on the sled. cos cos (240 N)(1.5 m s)(10.0 s)cos30.0 3.1 kJ W F r Tv t θ θ = Δ = Δ = ° = 13. Strategy The kinetic energy of the sack is equal to the work done on it by Sam. Use Eqs. (6-2), (6- 6), and (6-7). Solution (a) Compute the kinetic energy of the sack. 2 2 2 f i 1 1 ( ) 0 , so (2.0 N)(0.35 m) 0.70 J . 2 2 x K m v v mv K W F x K Δ = = = = = Δ = = (b) Solve for the speed of the sack. 2 1 2 2(0.70 J) , so 0.37 m s . 2 10.0 kg K K mv v m = = = = 26. (a) Strategy Use conservation of energy. Solution Find the speed of the cart as it passes point 3. 2 1 1 1 2 E mv = if 1 0 y = and 2 3 3 3 1 . 2 E mv mgy = + 2 2 f 3 3 3 i 1 1 1 1 , so 2 2 E E mv mgy E E mv = = + = = = 2 2 2 3 1 3 2 (20.0 m s) 2(9.81 m s )(10.0 m) 14.3 m s . v v gy = = = (b) Strategy Use the result of part (a), replacing 3 with 4. If the result is real—the argument of the square root is nonnegative—the cart will reach position 4. Solution Compute the speed of the cart at position 4.

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• Winter '08
• REHSE

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