Find the force acting to the right

1. Nov 26, 2014

Woolyabyss

1. The problem statement, all variables and given/known data
At time t = 0 s, a mass of 5 kg is moving to the right at 12 m/s.
Starting at t = 0 s, a
constant force is applied to the mass until it is brought to rest over a distance of 120 m.
Find the force acting to the right.

A [0 N]
B [3 N]
C [-3 N]
D [-3/5 N]
E [2 N]
2. Relevant equations
F = ma

3. The attempt at a solution
This is a question on a sample multiple choice quiz my lecturer gave me.
I'm torn between A and C it says find the force acting to the right but there is none. On the other hand the force acting relative to the right is -3N (taking the direction of its velocity as positive)

Any help would be appreciated.

2. Nov 26, 2014

haruspex

Yes, it isn't that well worded. In everyday English "the force acting to the right" would mean "of the forces, the one which is acting to the right". But here I'm reasonably sure it merely means taking right as positive.

3. Nov 26, 2014

Vicky Ramnarine

I believe it's A

4. Nov 27, 2014

CWatters

I vote C (-3N).

The mass is decelerating so there must be a net force to the left.
The magnitude calculates out at 3N.

If right is defined as positive then the net force acting to the right must be -3N.