Kaplan momentum question error?

[TommyTman]

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The question is as follows:

Assume that the piece with a piece with a mass of 1M kg is moving at 4 m/s. How much force is required to bring the piece to a complete stop in 3 seconds?

This is an impulse problem so I set up: Delta(p) = FDelta(t)
When I solve I get the answer (-4/3M)N
The Kaplan answer is (4/3)N, but considering Force is a vector and acceleration is in the opp. direction of velocity, wouldn't the force in fact be negative? Thanks.

 

[Blueprint MCAT Tutor]

Were there answer choices and was -4/3 an answer choice? Sounds like you're right to me.

 

[inasensegone]

You have calculated the answer correctly... force (and hence acceleration) must act opposite to the direction of motion if it is to stop the object. The only reason I can think that they wanted a positive number would be with their language. How much force [is needed]. Maybe if they felt like this implied they simply wanted the magnitude of the force, then that could explain it... however I would chalk this up to the idiosyncrasies of a test prep company and move on. You won't have such ambiguity on the real test.

 

[TommyTman]

Thanks alot guys. Yes, there was a -4/3 answer choice. I was thinking maybe I had looked at the question too long and was missing something obvious. It's a bummer when prep materials have wrong answers, it makes me start second guessing whether some things are right or not. I appreciate the input.

I botched the question too its "Assume that the piece with a mass of 1M kg"