A 3.3 kg wooden block is placed on 22 degree inclined plane and is connected by a string that passes over a light friciton less pulley at the top of the incline and then attached to a hanging 3.0kg block.If the coefficient of static friction bet the 1st block and the surface of the plane is 0.25 and coefficient of kinetic friction is 0.15

Question

a)which direction will the first block move, up the plane or down the plane if it does.
b)Calculate the acceleration of the system and the tension force in the string.

Answer 1

Draw the diagram. Next resolve the weight of the block into normal, and down the plane components.

Normal: mgCosTheta
downtheplane: mgSinTheta

Up the plane force is 3g

Friciton is mgCosTheta*mu

Now sum forces: Assume friction is down the plane.

Net force= totalmass*a
3g-mgSinTheta-mgCosTheta*mu= (3+3.3)a
solve for a. If a is zero, then you chose the wrong direction for friction, and you know answer a).

Answer 2

A doubly tethered model airplane of mass 1.0 kg is attached to a vertical rod by two very light strings that are 2.0 each in length. the airplane and the the strings rotate in a horizontal circleabout the rod with both the strings remaining taut.The attachment points of the strings are also separated by 2.0 m If the tension in the upper string is 39.2 N. Calculate
a)the tension in the lower string.Is it likely to be less or more than the tension in the upper string?
b)the steady speed of the ball as it undergoes circular motion.