Materials MCQs (set 2)

Two masses hang at rest from a spring, as shown in the diagram. The string separating the masses is burned through. Which of the following gives the accelerations of the two masses as the string breaks? [acceleration of free fall = g]

• acceleration of 1 kg mass upwards in m·s^-2: 3g, acceleration of 2 kg mass downwards in m·s^-2: g

• acceleration of 1 kg mass upwards in m·s^-2: 2g, acceleration of 2 kg mass downwards in m·s^-2: 2g

• acceleration of 1 kg mass upwards in m·s^-2: 2g, acceleration of 2 kg mass downwards in m·s^-2: g

• acceleration of 1 kg mass upwards in m·s^-2: g, acceleration of 2 kg mass downwards in m·s^-2: g

The equation for hydrostatic pressure, relating pressure to density, is p = hρg. How can both sides of this equation be written in terms of base units?

• [N·m^–1] = [m] [kg·m^–3] [m·s^–1]

• [N·m^–1] = [m] [kg·m^–3] [m·s^–2]

• [kg·m^–1·s^–2] = [m] [kg·m^–3] [m·s^–2]

• [kg·m^–1·s^–1] = [m] [kg·m^–1] [m·s^–2]

Which statement defines the density of a substance?

• the force per unit area acting on the substance

• the increase in length per unit length of the substance

• the mass per unit volume of the substance

• the work done per unit time by the substance

Hooke’s Law states that the extension of a material is proportional to the load, up to:

• the yield point

• the limit of proportionality

• the breaking point

• the elastic limit

A load of 3.0 N is attached to two springs of negligible mass joined in series. Each spring has a spring constant of 15 N·m^-1. What is the energy stored in the springs?

• 0.30 J

• 0.60 J

• 0.90 J

• 1.2 J

Two vertical copper wires X and Y of equal length are joined as shown. Y has a greater diameter than X. A weight W is hung from the lower end of Y. Which of the following is correct?

• The strain in X is the same as that in Y.

• The stress in Y is greater than that in X.

• The tension in Y is the same as that in X.

• The elastic energy stored in X is less than that stored in Y.

A load of 4.0 N is suspended from a parallel two-spring system as shown in the diagram. The spring constant of each spring is 20 N/m. The elastic energy stored in the system is...

• 0.10 J

• 0.20 J

• 0.40 J

• 0.80 J

A wire of length L and cross-sectional area A is stretched a distance e by a tensile force. The Young modulus of the material of the wire is E. Which expression gives the elastic energy stored in the stretched wire?

The overhead cables used to transmit electrical power by the National Grid usually consist of a central core of steel cables surrounded by a sheath of cables of low resistivity material, such as aluminum. What is the main purpose of the steel core?

• To force more current into the outer sheath.

• To provide additional current paths through the cables.

• To reduce the power lost from the cables.

• To increase the mechanical strength of the cables.

The diagram shows the atoms of a substance with the atoms at the corners of a cube. The average separation of the atoms at a particular temperature is 15 nm. When the temperature changes so that the average separation becomes 17 nm, by what factor will the density of the substance change?

• 0.61

• 0.69

• 0.78

• 0.88