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Transcript 
A team of dogs drags a 121 kg sled 1.72 km over a horizontal surface at a constant
speed. The coefficient of friction between the sled and the snow is 0.205. The
acceleration of gravity is 9.8 m/s. Find the work done by the dogs. Answer in units
of kJ.
N
F
Ffr
x
mg
πΉπ‘“π‘Ÿ – friction force
𝐹 – pulling force
Constant speed => acceleration equals 0.
Newton’s first law of motion:
π‘₯:
𝐹 = πΉπ‘“π‘Ÿ
𝑦:
𝑁 = π‘šπ‘”
Friction force equals πΉπ‘“π‘Ÿ = πœ‡π‘ = πœ‡π‘šπ‘”, πœ‡ - coefficient of friction.
Therefore:
𝐹 = πœ‡π‘šπ‘”
The work done by a constant force of magnitude F on a body that moves a
displacement d in the direction of the force is the product:
π‘Š = 𝐹𝑑 = πœ‡π‘šπ‘”π‘‘ = 0.205 βˆ— 121 π‘˜π‘” βˆ— 9.81
Answer: 419 π‘˜π½
π‘š
βˆ— 1720 π‘š = 419 π‘˜π½
𝑠2
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