Question

An object with a mass of `7 kg` is on a surface with a kinetic friction coefficient of `7`. How much force is necessary to accelerate the object horizontally at `28 m/s^2`?

Answer 1

I found: `676N`

Explanation:

Consider the diagram:

We can use Newton's Second Law: `SigmavecF=mveca`
on the `x` and `y` axis as:
`F-f=ma`
`N-W=0`
where:
`N` is the normal reaction;
`W` is the weight (`=mg`);
`f=mu_kN` is kinetic friction;
`a=28m/s^2` is acceleration.
So we get from the second that:
`N=W=mg`
into the first:
`F-mu_k*mg=ma`
`F-(7*7*9.8)=7*28`
so:
`F=196+480.2=676.2~~676N`