VISUAL PHYSICS ONLINE

2 DYNAMICS

P20 015

A 4.00 kg object rests on a smooth surface hinged at the point A. A block on the surface prevents the object from sliding. The 4.00 kg object is attached by a light, inextensible string to a 3.00 kg object hanging vertically over a frictionless pulley. The smooth surface is gradually lowered, changing the angle q, until the two objects begin to accelerate.

a) Determine the tension in the string before the objects start to move.

b) At what angle do the objects start to move?

c) Calculate the magnitude of the acceleration of the objects when the surface is inclined at an angle of 20.0^o.

View solution below only after you have completed the answering the question.

Solution

(a)

Let the 3.00 kg object be System B and that it is in equilibrium.

(b)

Let system A be the 4.00 kg object and System B be the 3.00 kg object. The two objects are joined together by an extensible cord, hence they must move with the same magnitude of acceleration a.

Therefore, the objects will only start to accelerate when the angle of the incline is less than 48.6^o.

(c)

When the angle of the incline is we can calculate both the string tension and acceleration of the two objects.