Problem 1: (a) Ã= 3â – 2ŷ, B = 4ây – 5ŷ. Ã · B =? Answer: 22 (b) Ã = -2ô + 4, B = 3â – lŷ. Ả.B =? Answer: –10 (c) Ã = 5â – 3ŷ, B = -3â – 5ŷ. Ã. B =? Answer: 0 d = 4m F = 20 N 0=30° 4 kg m = . m = 2 kg HK = 0.5 F = 40 N Hk = 0.2 0 = 30° Problem 2: In the figure above on the left we have a force F = 20 N pulling a box to the right at an angle 0 = 30° above the horizontal. The box has a mass m = 2 kg, the coefficient of kinetic firction between the box and the ground is uk = 0.2, and the block moves a distance d = 4 m to the right. (a) What is the work done by the force F? Answer: 69.3 J (b) What is the normal force from the ground? Use g = 10 m/sec2 Answer: 10 N (c) What is the work done by the kinetic friction force? Answer: -8 J (d) What is Wnet, the net work done on the box? Answer: 61.3 J (e) The box has an initial speed of 4 m/sec. What is the speed of the box after it has travelled the distance d = 4 m? Answer: 8.8 m/sec
Problem 1: (a) Ã= 3â – 2ŷ, B = 4ây – 5ŷ. Ã · B =? Answer: 22 (b) Ã = -2ô + 4, B = 3â – lŷ. Ả.B =? Answer: –10 (c) Ã = 5â – 3ŷ, B = -3â – 5ŷ. Ã. B =? Answer: 0 d = 4m F = 20 N 0=30° 4 kg m = . m = 2 kg HK = 0.5 F = 40 N Hk = 0.2 0 = 30° Problem 2: In the figure above on the left we have a force F = 20 N pulling a box to the right at an angle 0 = 30° above the horizontal. The box has a mass m = 2 kg, the coefficient of kinetic firction between the box and the ground is uk = 0.2, and the block moves a distance d = 4 m to the right. (a) What is the work done by the force F? Answer: 69.3 J (b) What is the normal force from the ground? Use g = 10 m/sec2 Answer: 10 N (c) What is the work done by the kinetic friction force? Answer: -8 J (d) What is Wnet, the net work done on the box? Answer: 61.3 J (e) The box has an initial speed of 4 m/sec. What is the speed of the box after it has travelled the distance d = 4 m? Answer: 8.8 m/sec
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