Answer: 1.15 m/s²
Explanation:
First, let's find the net force that the box experiences:
F = Applied force - friction force
F = 30 N - 21 N
F = 9 N
Now, we can use Newton's second law of motion to find the acceleration of the box:
F = ma, where m is the mass and a is the acceleration.
Substituting the net force and mass of the box:
9 = 7.8a
Solve for a:
a = 9/7.8
a = 1.15 m/s²
The acceleration of the box is 1.15 m/s².
