CE Phy mechanics

1.點解voltage(電壓)唔係vector(向量),唔係有+同-架咩
The (+) and (-) affixed to voltage indicates its magnitude, NOT the direction. As voltage can have value below reference (earth) potential (i.e. 0 volt), thus a -ve voltage does exist.

2.thrust of the rocket即係=net force of the rocket?
No. Generally, the thrust refers to the "force given by the rocket engine". It is NOT the net force on the rocket.

3.畫free-body diagram(隔離體圖)需不需要畫地下?
No. The earth is usually not involved in the free diagram of any object.

4.有個掛牌,有2條繩,一條連住天花板,一條連住牆,條繩同天花板係perpendicular,條繩同牆又係perpendicular,咁係咪個兩條繩都有tension
If the plate is vertical and in equilbrium, the tension on the string fixed to the wall should have no tension.

5.moving object 有冇impulse(衝量)?
No. Impulse would give a change in momentum. There is no impulse on an object moving with constant velocity, as thers is no change of momentum at all.

6.explosion(自爆)total KE會增加?
Explosion involves a production of energy. Any object will increase in kinetic energy if there is an explosion occurs.