ACT Science Practice Test 38

Students studying mirrors and reflection were given the following information:

There is a definite relationship between image characteristics and the distance an object is placed with regard to a concave mirror (see Figure 1). If an object is located beyond the center of curvature (C), its reflected image will be inverted (upside down) and smaller than the object itself. If an object is located precisely at C, the image will also be located at C; it will appear inverted and true to the object’s actual size. When the object is placed between C and the focal length (F), the image will be inverted and larger than the object. When the object is located precisely at F, no image is formed whatsoever. Lastly, if an object is placed between F and the mirror, its image will appear upright and larger than the object.

Figure 1

Given no further information, the students were asked to explain how the following magic trick is performed:

A famous Chinese magician conducts a classic magic trick utilizing a concave mirror with a focal length (F) of 1.6 m and a center of curvature (C) of 2.2 m. He is able to utilize the mirror in such a manner as to produce an image of a light bulb at the same location and of the same size as the actual light bulb itself.

Student 1

The light bulb must have been placed exactly 1.6 m in front of the mirror, creating a perfect reflection. The image would thus be in the same location as the light bulb, have the same dimensions as the light bulb, and be an upright image.

Student 2

The light bulb must have been placed exactly 2.2 m in front of the mirror. The image would then be in the same location and have the same dimensions as the actual light bulb, although it would be inverted.

Friction is the force that resists movement when two surfaces are in contact and is represented by F_f. The coefficient of friction (COF, symbolized by μ) is a quantity used to measure the force of friction based on the normal force (F_N). There are two COF’s for a given surface-to-surface contact: static COF (μ_s) and kinetic COF (μ_k). μ_s is used for objects at rest and μ_k is used for objects in motion. The normal force is an upward force, perpendicular to the surface the object is either resting on or moving on.

The basic equation for calculating the coefficient of friction is:

Figure 1 is a diagram of a block resting on an inclined plane. The forces shown are defined above. F_G represents the force of gravity.

Figure 1

Scientists performed an experiment using several different materials to determine μ_s and μ_k for each pair of materials. Figures 2 and 3 show the results.

Figure 2

Figure 3

The main source of the world’s energy for the last century has been fossil fuels. To use fossil fuels, we must be able to locate and recover them at affordable costs, convert them to usable forms, and use them without wasting them or harming the environment.

Experiment 1

Scientists set out to determine the energy potential of various fossil fuels. They burned 1 ton of each of 5 different fuel varieties, and measured the energy produced. Table 1 shows the energy content of various fossil fuels.

Table 1

Experiment 2

Students completed an experiment to measure the heat energy obtained from natural gas, using water, a Fahrenheit thermometer, and a Bunsen burner (see Figure 1). They filled a beaker with enough water to

Figure 1

weigh 1 pound (approximately 450 mL). They recorded the temperature of the water, then lit the Bunsen burner and stirred the water continuously. They took several measurements of the water’s temperature, at 5-minute intervals. The results of the experiment are displayed in Table 2.

Table 2

Each type of fossil fuel releases a different amount of energy. This energy is measured in a variety of units. Table 3 provides a conversion chart for energy units.

Table 3

The growth of tumor cells in a culture depends on the amount of nutrients in the culture. Cell production can be determined by counting the number of cells. The effects of various concentrations of glucose and calcium on the growth of three different cell types were tested. Each culture dish began the test with 0.5 million cells, to which was added a solution containing known concentrations of either glucose or calcium. The results after three days are shown in Figures 1 and 2.

Figure 1

Figure 2