# Velocity in certain direction[components]

1. Oct 12, 2011

### anigeo

could you please tell me why the velocity of the block M along the horizontal direction is v/sinθ and not vsinθ as in the case of components of vectors?

#### Attached Files:

• ###### Untitled.jpg
File size:
6.8 KB
Views:
46
2. Oct 12, 2011

### Staff: Mentor

If I understand your diagram (the block is being dragged by the string along the surface), v is the rate at which the string is being pulled. To relate the speed of the block along the surface to the rate at which the string moves, consider the right triangle formed by the block and the string. Let x be the horizontal distance from block to pulley and z be the length of string between block and pulley. How can you relate those quantities?

3. Oct 12, 2011

### anigeo

ok i understand what u say. actually this is also what i thought.so thanks.
but while taking the component of a vector along a direction θ from it we write vcosθ if v is the vector.why is it not applicable here?

4. Oct 12, 2011

### Staff: Mentor

The block moves along the horizontal. It's the component of the block's velocity (VB) in the direction of the string that must equal the rate at which the string is pulled:
VB sinθ = v

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook