answer questions 5 and 6 explain 5. A 40 N crate rests on a rough horizontal flo

Question

answer questions 5 and 6 explain

5. A 40 N crate rests on a rough horizontal floor. A 12-N force is then applied to it. If the coefficients of fiiction are u 0.5 and uk 0.4, the magnitude of the frictional force on the crate is: A) 8 Ni B) 12, N C) 16 N D) 20 N E) 40 N 6. Camping equipment weighing 6000 N is pulled across a frozen lake by means of a horizontal The coefficient of kinetic fiiction is 0.05. The work done by the campers in pulling the equipment 1000 m at constant velocity is: A) 0 J B) 1.5 x 103 J c) 3.0 x 10' J D) 2.9 x 10 J E) 6.0 x 10 J

Explanation / Answer

Weight of crate, W= mg = 40 N

So, m = 40/g = 40/9.8 = 4.08 kg

Minimum force required to move the body, F_min = us*m*g = 0.5*4.08*9.8 = 19.99 N

But applied force = 12 N

So, the body wont move and thus the frction must be equal and opposite to the applied force ,

So, friction = 12 N <------------answer

2)

W = mg = 6000

So, m = 6000/9.8 = 612.2 kg

Now, friction, f = uk*m*g = 0.05*612.2*9.8 = 300 N

As the equipment moves with constant velocity , thus the net force must be 0

Thus the applied force must be equal and opposite to friction

So, applied force = 300 N

So, work done by campers = F*d

where d = distance traveled = 1000 m

So, Work done = 300*1000 = 3*10^5 J <--------answer

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