Two blocks are connected by a string passing a frictionless pulley. The inclined plane is smooth. If the block of A (mass= m) goes down a distance h , which of the following statement is / are correct ? (A is suspended , B is on the slope(mass=M). )
(1) the potential energy lost by A is mgh .
(2) the PE gained by B is Mgh .
A (1) B(1) and (2)
the answer is A . Why ? Why not B ?
oh....
2007-03-14 7:34 pm
回答 (2)
2007-03-14 7:49 pm
✔ 最佳答案
因為 B 唔係 suspended (半天吊), 而係係個斜枱上面, 吊住 B 的那部份繩因為斜枱的關係, 角度會變, 而令到 B 未必同樣升高 h 咁多, 所以 B 升高的高度唔保証係 h, 答案 (2) 咪唔啱囉!
2007-03-15 1:40 am
By law of conservation of energy, the potential energy (PE) lost by A must be equal to the PE gained by B.
Unless the masses m and M are equal, m(gh) can never be equal to M(gh).
Unless the masses m and M are equal, m(gh) can never be equal to M(gh).
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