# Force and acceleration

Here is a problem from our freshman physics homework--it seemed pretty simple and self-explanatory:
(refering to a diagram) 22.5 newtons of force must be used to pull the 4 kg block across the rough surface at a constant velocity of 6.7 m/sec to the right. If the string pulling the block rightward were to break, what would be...
(a) the acceleration of the block:
Now, isn't the formula for acceleration a=F/m?
Wouldn't a = 22.5N/4kg = 5.625 m/s^2??? It seems simple enough, yet it is marked wrong. If I made a silly mistake, I would like to know why, because it seems really easy and I don't know where I went wrong.
THEN, after that, it prompts me to find the time it would take for the block to stop. Not quite sure how to figure that out... any suggestions?

Hootenanny
Staff Emeritus
Gold Member
oooo said:
Wouldn't a = 22.5N/4kg = 5.625 m/s^2???

Nope. What is the direction of the force acting relative to the velocity of the block?
HINT: You are very close.

~H

Last edited:
ooh, so it is -5.625! Thanks!
OH! and about my time question, I thought about it some more and I figured it out (no need to help) but thanks though!

Hootenanny
Staff Emeritus