Question 30 Answer and Explanation _ACT December 2020 Form D03 Science Section

Passage V

The Atwood machine shown in Figure 1 was used as part of 2 studies on objects moving with constant acceleration.

Study 1

In each of 10 trials, the following procedure was performed:

1. A string was passed over 2 pulleys. The string had a ring on each end and a spring scale (a device that can measure forces) near one end.

2. Block X, having a mass m_X, was hooked onto the left ring. Block Y, having a mass m_Y, was hooked onto the right ring.

3. Block X was pulled down and held in place so that Block Y was 1.5 m above the platform.

4. With all objects starting at rest, Block X was released, and both F (the force on the string) and t (the time required for Block Y to fall to the platform) were measured.

(Note: All objects other than the 2 blocks had negligible mass. The string was not stretchable.)

Table 1 shows the results, with F in newtons (N) and t in seconds (s).

Study 2

The acceleration, a, of Block Y in each trial of Study 1 was then calculated using the available t data. Table 2 shows the results, with a in meters per second squared (m/s²).

30. Suppose that in Step 3, Block X had been pulled down and held in place so that Block Y was 100 centimeters (NOT meters) above the platform. Would the values of t recorded in Study 1 more likely have been greater than or less than those shown in Table 1 ?

F. Greater, because Block Y would have fallen a longer distance.

G. Greater, because Block Y would have fallen a shorter distance.

H. Less, because Block Y would have fallen a longer distance.

J. Less, because Block Y would have fallen a shorter distance.

Answer and Explanation

Your Answer is

Correct Answer is J

Explanation

In the question stem, it is said that Block Y should not land, but let it stop at a distance of 100 cm from the ground. Because the distance of movement is shortened, the time must be reduced accordingly.