關於物理的簡單問題

1. In an experiment to measure the half-life of a radioactive isotope in a place where the background count rate is 20 counts per minute, the following results are recorded:




Time/ minute

0

2

4

6

8

10

12


Total count rate/ counts per minute

116

96

80

69

58

50

44

The half-life is about
A. 6 minutes
B. 8 minutes
C. 10 minutes
D. 12 minutes

2. As shown in the figure, a 3-kg mass is being pulled by a string such that the mass is accelerating uniformly to the right. Suddenly, the string breaks. Estimate the acceleration of the mass just before the string breaks, given that the maximum tension in the string is 200 N.

A. 56.7 ms-2
B. 65.9 ms-2
C. 67.4 ms-2
D. 76.7 ms-2

http://i617.photobucket.com/albums/tt257/michaelcoco_/4.jpg

3. A block is projected up along an inclined plane. Its velocity-time graph (v-t graph) is shown as the dashed line. When the mass of the block is doubled, which of the following graphs best represents the new v-t graph (solid line) for the doubled mass? Assume other conditions remain unchanged.

http://i617.photobucket.com/albums/tt257/michaelcoco_/5.jpg

※試列明計算步驟及各點對與錯之原因※