✔ 最佳答案
95.3. The answer is A.
The trolley and the Earth is considered to be one system.
In this system, there is no external force acting on it. The compression force in the spring is considered as an internal force in the system. So, the momentum of the system conserves.
So, the answer is A.
B is not correct, this should be the energy of the trolley, not momentum.
C and D are not correct, it is also the energy, not momentum.
For E, there is no evidence showing the collision is not perfectly elastic.
00.6. The answer is A.
By Newton's 2nd law of motion,
F = ma = 2ma'
a/a' = 2/1
So, For the same period of time, the final velocity, v/v' = 2/1 (You can use v = at)
So, the ratio of gain in K.E.
= 1/2 mv2 : 1/2 (2m)v'2
= 2 : 1
03.5. The answer is A.
Maximum compression occurs when the two blocks have no relative velocity to each other.
Just imagine when P moves faster than Q, then there will be more compression afterwards.
And when P moves slower than Q, then the compression will become less.
04.2. C
You can derive it by conservation of momentum and energy.
07.2. The answer is A.
For the block to move with uniform velocity, there is no external horizontal force acting on the system.
So, the floor just have to apply a reaction equals to (M + m)g to support the weight of the two objects.
2009-07-02 23:15:44 補充：
cos0 = 1, so you are right
2009-07-04 09:31:37 補充：
We should not resolve the components of R, instead we should ressolve the component of mg.
