# Homework Help: How to work out this Acceleration

1. May 25, 2010

### koyabr

1. The problem statement, all variables and given/known data

Ive posted relevant picture.No thought for any friction.The ramps mass is M,and the cubic sliders is m.Release the slider(no initial speed),Whats the Acceleration(relative to the earth) of it?

2. Relevant equations

Ive been told the answer,as is showed in the picture.But I cant work out it for myself.

3. The attempt at a solution

I got stuck when Ive brought in too many parameters,I might have mistaken something.

Im a new comer and English beginner,hope Ive described the question clearly.Thanks for viewing.:)
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### 10935341.jpg
File size:
4.1 KB
Views:
126
2. May 25, 2010

Remember Newton's 3rd Law of Motion, for every action there is an equal and opposite reaction, meaning:

Think about this given situation at a stand-still, where the block is on the ramp at the top but nothing moves (because everything is starting from rest). There is no motion, correct?

Gravity then pulls the block down the ramp, which then causes the ramp to move as well (remember, everything started from rest, aka net F=0 initially). If the intial net F=0, then the final net F must equal 0 as well, agreed? With the understanding of the fact that momentum is conserved, you must solve for the net horizontal force on the block (horizontal to the ground surface that the ramp is not, not horizontal to the ramp itself). This must also equal the net horiziontal force on the ramp caused by the block. Setting these two equal should be your method of solving for a.

3. May 26, 2010

### koyabr

Thank EngineerHead and I think Iv figured out the process,the most disturbing thing is the resultant force of the block,whose direction & size are not so clear.I tried the vector triangle,and found the sine theorem useful in working out the resultant forces size.

Astonishing enough,I got a different answer from whats showed in the picture,perhaps I have to consult the question provider.