Acceleration of an object given forces

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1. Jul 14, 2016

Zack K

1. The problem statement, all variables and given/known data
An 85 kg tobbogan that was originally accelerating at 3.0 m/s2 on frictionless snow hits a bare patch of concrete that exerts a force of friction on the sled of 180 N, what will the new acceleration be?

2. Relevant equations
F=ma

3. The attempt at a solution
Ok so this was originally a 2 part question but I merged it into one. I already calculated the applied force of the tobbogan on frictionless snow which is 255 N east. Now I have to find its acceleration when it hits the concrete. So I got the Fnet by subtracting the applied force by the force of friction. 255-180= 75 N east. So now I do a=F/m. So the acceleration by my understanding should be 75/85 which is 0.88 m/s2. But the answer sheet says that it is 0.94 m/s2.

Last edited: Jul 14, 2016
2. Jul 14, 2016

Orodruin

Staff Emeritus
Your method and aithmetic seem correct. This may be a typo in the answer key.

In the future, please quote the question exactly as stated without making any changes. Many times we get questions from students that have misinterpreted the question.

3. Jul 14, 2016

CWatters

=45N not that it helps.

I suggest you post the question word for word in case there is something you missed when you merged it into one question.

4. Jul 14, 2016

haruspex

CWatters asked for the original unmerged question. You seem to have just reposted your merged version.
In particular, if any of the input numbers you quote in the merged version are actually results calculated for the first part of the question, they may contain rounding errors that become significant in the second stage.

5. Jul 14, 2016

Zack K

225
Sorry I accidentally posted that and am trying to delete it. I don't know how to delete. Also the answer I got was a whole number. No rounding was required

6. Jul 14, 2016

CWatters

No problem. I didn't notice that 3*85 is 255 not 225.

7. Jul 14, 2016

Zack K

Thanks guys for the help. I'm assuming that the answer key had a typo.

8. Jul 14, 2016

Orodruin

Staff Emeritus
You cannot. Please use the report feature if this happens and a mentor can delete the post for you as I have done.