# Friction and Pulleys

BvU
Homework Helper
2019 Award
That is still saying the block moved by 1 meter ( well, not really, but never mind (*) ). Is it also what you mean to say ?

Would it help you if you made a drawing of the intial situation and one of the situation where the flat car has moved over some distance ?

Or perhaps you do a little experiment where you attach a wire to a fixed point (the wall) on one end and to some object (the block) on the other. Let you finger play the role of the pulley and move your finger by 10 cm. How far did the object move ?

(*) you can easily see that can't be right: imagine the car is fifty meters long and moves by 1 m. No way the block is "where the pulley was".

It is one metre closer to the pulley
That's why I answered that Distance covered by block would be equal to shorter length of string(the region of string which connects block and pulley).That is block will reach where pulley was.

It is one metre closer to the pulley.
How to interpret it.

BvU
Homework Helper
2019 Award
If the pulley moves 1 m away from the wall, it has to reel in the block by 1 m. So the pulley moves 1 m and pulls in the block by 1m. Over what distance has the block moved wrt the wall ?

The length itself of the shorter section has nothing to do with it. It's about how much that length has changed that's relevant.

It's about how much that length has changed .
1 meter?

So the pulley is one metre further from the wall,
Does that mean distance between wall and pulley is 1 meter?

BvU
Homework Helper
2019 Award
Yes, that length has changed 1 meter: the pulley reeled it in by 1 meter. he pulley itself moved by 1 meter. How much has the block moved wrt the wall ? • gracy
BvU
Homework Helper
2019 Award
No, distance between pulley and wall is not one meter. It has changed by 1 meter. If it was 10 m before, it now is 11 m.

How much has the block moved wrt the wall ?
2 meter?

BvU
Homework Helper
2019 Award
Hurray ! (but: why the ? question mark?)
So, to summarize the last umpteen posts: when the cart moves 1 thing, the block moves 2 things (meters, inches, millimeters, whatever distance).

Now, next step: if the cart is accelerated by 3 m/s2, what must be the acceleration of the block ?

• gracy
haruspex
Homework Helper
Gold Member
2 meter?
Hooray!
So for each metre the car moves, the block moves 2 m.
If the car's acceleration is a, what is the block's acceleration?

• gracy
BvU
Homework Helper
2019 Award
• gracy
acceleration of the block =2 multiplied by trucks acceleration
i.e 6 m/s^2

So T-150=30 multiplied by6
T=330 N

Bedtime for me
Even I am going to sleep.

haruspex
Homework Helper
Gold Member
So T-150=30 multiplied by6
T=330 N
You got it. Sleep well.

• gracy
"haruspex" and BVU bigThanks for all your answers .And BVU sorry for that question mark You both are true homework helper.BVU you used the whiteboard so nicely.Very neat diagram
.Next time when Calculus master will visit physics forum,will get homework done.  if the acceleration of the block = 2 * truck acceleration, then the force required in the string = m * a