Exam 12: Equilibrium and Elasticity

Three identical uniform rods are each acted on by two or more forces, all perpendicular to the rods. Which of the rods could be in static equilibrium if an additional force is applied at the center of mass of the rod?

Young's modulus can be used to calculate the strain for a stress that is:

For a body to be equilibrium under the combined action of several forces:

The bulk modulus is a proportionality constant that relates the pressure acting on an object to:

Strain can be measured in:

Stress can be measured in:

A 160-N child sits on a light swing and is pulled back and held with a horizontal force of 100 N. The magnitude of the tension force of each of the two supporting ropes is:

The ultimate strength of a sample is the stress at which the sample:

The 600-N ball shown is suspended on a string AB and rests against the frictionless vertical wall. The string makes an angle of 30 $\degree$ with the wall. The ball presses against the wall with a force of magnitude:

A 4.0 m steel beam with a cross sectional area of 1.0 *10^-2 m² and a Young's modulus of 2.0 * 10¹¹ N/m² is wedged horizontally between two vertical walls. In order to wedge the beam, it is compressed by 0.020 mm. If the coefficient of static friction between the beam and the walls is 0.70, the maximum mass (including its own) it can bear without slipping is:

A window washer attempts to lean a ladder against a frictionless wall. He finds that the ladder slips on the ground when it is placed at an angle of less than 75 $\degree$ to the ground but remains in place when the angle is greater than 75 $\degree$ . The coefficient of static friction between the ladder and the ground:

Young's modulus can be correctly given in:

A uniform plank XY is supported by two equal 120-N forces at X and Y, as shown. The support at X is then moved to Z (half-way to the plank center). The supporting forces at Y and Z are then:

A cylinder placed so it can roll on a horizontal table top, with its center of gravity above its geometrical center, is:

For a body to be equilibrium under the combined action of several forces:

The conditions that the sum of forces and the sum of the torques both vanish:

A 960-N block is suspended as shown. The beam AB is weightless and is hinged to the wall at A. The tension force of the cable BC has magnitude:

A meter stick on a horizontal frictionless table top is pivoted at the 80-cm mark. A force is applied perpendicularly to the end of the stick at 0 cm, as shown. A second force (not shown) is applied perpendicularly at the 60-cm mark. The forces are horizontal. If the stick does not move, the force exerted by the pivot on the stick:

For an object in equilibrium the sum of the torques acting on it vanishes only if each torque is calculated about:

The ideal mechanical advantage (i.e. the ratio of the weight W to the pull P for equilibrium) of the combination of pulleys shown is: