7. An engine is used to pull a train of two cars out of a mine. The floor of the

Question

7. An engine is used to pull a train of two cars out of a mine. The floor of the mine slopes upward at an angle of 30°. Each car has a mass of 104 kg and normally travels without friction on the tracks. The engine can exert a maximum force of 1.5.10 N on car A. a. The engine first accelerates the cars from rest by exerting its maximum force What is the acceleration of the cars? b. Once the train has reached a reasonable speed, the engineer throttles back so that they continue at a constant speed. Now what force does the engine exert on car A? c. What is the tension in the massless, straight chain connecting cars A and B while they are travelling at a constant speed? | -300

Explanation / Answer

7. (A) on car A and B , along the incline,

Fnet = m a

F _ engine - (mA + mB)g sin30 = (mA + mB)a

(1.5 x 10^5) - (2 x 10^4)(9.8) sin30 = (2 x 10^4) a

a = 2.6 m/s^2 ....Ans

(B) for constant speed, a= 0  

Fnet = F - (2 x 10^4)(9.8) sin30 = 0

F = 9.8 x 10^4 N

(C) then on car B,

Fnet = 0

Fnet = T - mB g sin30 = T - (10^4)(9.8)sin30 = 0  

T = 4.9 x 10^4 N

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