ACT science practice test 56

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


Astronomers have identified more than 170 moons in the solar system. For centuries, many of these scientists have used telescopic observations to measure the time it takes each moon to complete each orbit (the period). Using proportions and geometry, the radius of each orbit has also been determined. With these data in place, the speed of each moon in its orbit may be found by taking the circumference of each orbit (2 × π × radius, assuming a circular orbit, with π, or pi, approximately equal to 3.14159) divided by the period. The acceleration of each moon in its respective orbit is equivalent to its centripetal acceleration, which is found by dividing the square of its speed by the radius of its orbit. Table 10.4 provides data for various moons in our solar system.

TABLE 10.4

In an attempt to find the relationships in the data, the gravitational acceleration versus the inverse of the orbital radius squared was graphed in Figure 10.3.

Figure 10.3

1. Which moon has a period closest in value to the period of Earth's moon?

A. Andrastea
B. Miranda
C. Rhea
D. Hyperion

2. Given just the data in the table, which two moons are most appropriate for studying the effect of central planet mass on gravitational acceleration?

A. The moon and Atlas
B. Andrastea and Miranda
C. Atlas and Phoebe
D. Iapetus and Arial

3. What is the best description of the relationship between radius of orbit and the period of the moon?

A. The period is independent of the radius of orbit.
B. The period has no consistent relationship with the radius of orbit.
C. The larger the radius of orbit, the less the period.
D. The larger the radius of orbit, the greater the period.

4. Figure 10.3 indicates that the gravitational acceleration of moons is:

A. inversely proportional to the square of the radius.
B. directly proportional to the radius.
C. directly proportional to the square of the radius.
D. independent of planet mass.

5. A particular moon orbits a planet that is 318 times more massive than Earth. If that moon has a radius of orbit of 422 million meters, what is a possible value for the moon's speed?

A. 52 km/s
B. 31 km/s
C. 26 km/s
D. 17 km/s

6. Using Figure 10.3, along with information in Table 10.4, what conclusion can be made about the effect of a planet's mass on the acceleration of its moons?

A. Greater planet masses result in greater gravitational acceleration.
B. Greater planet masses result in lesser gravitational acceleration.
C. Gravitational acceleration is independent of planet mass.
D. Gravitational acceleration is directly proportional to the inverse-square of planet mass.

7. According to the passage, which columns were calculated from data gathered by scientists?

A. Period of moon orbit and central planet mass
B. Central planet mass and radius of orbit
C. Speed and gravitational acceleration
D. Gravitational acceleration and period

8. About how many times does the moon orbit the earth while Phoebe completes one orbit of Saturn?

A. 1.7
B. 34
C. 20
D. 27

9. How far does Helene travel in 15 seconds?

A. 10 km
B. 41 km
C. 150 km
D. 2,400 km

10. If the moons of Mars (a planet with a mass 0.107 times that of Earth) were placed on the graph in Figure 10.3, where would they most likely appear?

A. Above the line for the moons of Jupiter
B. Below the line for the moons of Jupiter but above the line for the moons of Saturn
C. Above the line for the moons of Jupiter initially, but then below that same line
D. Below the line for the moons of Saturn