物理一題 (已補圖)

[匿名]

2010-01-24 11:57 pm

Question 1
(a) A 4 kg ball throws up from the ground level with a velocity of 5 ms-1.
(i) Find the initial K.E.
(ii) If no energy loss, find the maximum height it can reach.

(b) A rod of length = L with the loads is in balance condition.
Assuming the weight of the rod is at its center, calculate the mass of the Box A.

(c) Three resistors are connected in series in a circuit as below, calculate
(i) the total resistance,
(ii) current output from power supply,
(iii) voltage across the 5 W resistor.

2 W 5 W 8 W
12 V power supply

http://img704.imageshack.us/img704/36/25347702.png --- Box A

http://img691.imageshack.us/img691/7284/59440801.png --- about(c)

回答 (2)

用戶18354

2010-01-30 12:03 am

無最佳解答

👍 0 👎 0

天同

2010-01-25 3:50 am

(b) since the rod is in balance, counter-clockwise moment = clockwise moment
hence, take moment about the pivot,
20 x 0.2L = 1.5 x 0.3L + M.(0.3+0.5)L
hence L = 4.44 kg

(c) (i) total resistance = (2+5+8) ohms = 15 ohms

(ii) Current = voltage/ resistance = 12/15 A = 0.8 A
(iii) Voltage across 5-ohm resistor = (0.8 x 5) v = 4 v

For Q1, I have already given you the answer before.

2010-01-24 19:52:04 補充：
Part (a)
http://hk.knowledge.yahoo.com/question/question?qid=7010012301709

👍 0 👎 0