Consider the total work done on an object that has several forces acting on it.

Question

Consider the total work done on an object that has several forces acting on it. A tractor is hitched to a sled loaded with firewood and pulls the sled a distance of 20.0 m along level frozen ground. Let’s determine what actually happened to the work energy produced by the forces acting on the sled. The free-body diagram is shown in (Figure 1) . We find that the total work done on the sled by all the forces is 10.0 kJ, so the kinetic energy of the sled must increase by 10.0 kJ. The mass of the sled ism=(14,700N)/(9.80m/s2)=1500kg. Suppose the sled’s initial speed vi is 2.00 m/s. What is its final speed?

Part A - Practice Problem:

If the tractor pulls horizontally and the friction force has a magnitude of 4400 N , what is the magnitude of the force the tractor must exert to make the sled move with constant speed?

Express your answer in newtons to two significant figures.

Explanation / Answer

Mass of the sled is 1500 kg

Increase in kinetic energy = 10 k j = 10000 j

Initial speed = 2 m /s

InInitial kinetic energy = 0.5 × 1500× 22 = 3000 j

Final kinetic energy = 3000 + 10000 = 13000 j

Now.   

   13000 = 0.5× 1500 × V2

Or. V = 4.16 m/s

Now fritcion fforce = 4400 ,N

Hence the traictor must overcome it.

FFor constant speed force of tractor = 4400 N

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