關於物理的簡單問題 - Ans.fyi 參考答案

關於物理的簡單問題

Tieria

2010-04-04 2:25 am

1. A 1000-kg truck is moving up in an inclined frictionless road with constant velocity of 10 ms-1. The road makes 300 with the horizontal. Which of the following statements is / are correct?
(1) The KE of the truck increases at the rate of 50 kJs-1.
(2) The PE of the truck increases at the rate of 50 kJs-1.
(3) Power output of the truck engine is 50 kW.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)

2. A wave is generated on a string. The waveforms at time = 0 s and 2 s are shown in the figure. Which of the following is / are correct?

(1) The frequency of the wave is 2 s-1.
(2) Particle B is moving up at time = 2 s.
(3) The motion of particle B and that of particle C are in antiphase.
A. (2) only
B. (1) and (2) only
C. (1) and (3) only
D. (2) and (3) only

http://i617.photobucket.com/albums/tt257/michaelcoco_/1.jpg

※試列明計算步驟及各點對與錯之原因※

回答 (1)

天同

2010-04-04 3:28 am

✔ 最佳答案

1. Statement (1) is wrong.
The truck is at constant speed. The KE of which would not be changed.

Statement (2) is correct.
The increase of vertical height in 1 s = 10.sin(30) m = 5 m
hence, increase of PE in 1 s = 1000g x 5 J = 50 000 J = 50 kJ
where g is the acceleration due to gravity, taken to be 10 m/s2
Statement (3) is correct.
Power output = work done in 1 s = increase in PE in 1 s = 50 kJ/s = 50 kw

2. Statement (1) is wrong.
Since only 1 complete cycle is generated in 2 s, the frequency of the wave is 1 Hz

Statement (2) is correct.
The wave travels from left to right. A crest is approaching particle B, hence it is moving upward.

Statement (3) is wrong.
The motion of 2 particles are in antiphase when they are half a wavelength apart. Since particles B and C are only 1/4 wavelength apart, they are not in antiphase.

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