Question

Mary applies a force of 71 N to push a box with an acceleration of 0.54 m/s2. When she increases the pushing force to 80 N, the box's acceleration changes to 0.69 m/s2. (a) What is the mass of the box?

There is a constant friction force present between the floor and the box.

Answer 1

I got `60kg`

Explanation:

We can use Newton's second law where the resultant of all forces is equal to mass times acceleration.
`71-f=m*0.54`
`80-f=m*0.69`
Where `f` is the constant friction.
From the first equation we have:
`f=71-0.54m`
Substitute into the second equation:
`80-71+0.54m=0.69m`
`0.15m=9`
`m=9/0.15=60kg`