Block A has weight 300N and Block B has 50N . Determine the distance B must raise from rest before A obtains Speed of 2.5m/s. Neglect mass of cord and pulley

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Borys Shumyatskiy | College Teacher | (Level 3) Associate Educator

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Hello!

The forces acting on the block A at any given moment are the gravity force which is equal to 300N down, and the weight of the block B ("transmitted" via the cord and the pulleys) up (50N).

The net force F is constant (300-50=250N) and acts downward. It gives the block the constant acceleration of F/m by Newton's second law. m is the mass of the block A and it is equal to its weight 300N divided by g (the gravity acceleration).

Therefore the speed will be (F/m)*t (t is for time).

The equation for t is

[F/(300/g)]*t = 2.5,

so t=2.5*300/(250*9.8)= approx. 0.306(s). The distance travelled by the block A (or the block B) will be (g*t^2)/2= approx. 0.459(m).

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