Answer: Fn
Explanation: Because Fn is applying force upward
Let us use the formula for Newton's Second Law of Motion:
Net force = Mass*Acceleration
Net force = Applied Force - μ*Normal Force
where μ is the coefficient of kinetic friction
Normal Force = Force due to gravity = mass*gravity
Normal Force = (210 kg)(9.81 m/s²) =<em> 2,060.1 N</em>
Then,
Net force = 4100 - 0.38*2060.1 = 3317.162 N
3317.162 N = (210 kg)(a)
Solving for acceleration,
<em>a = 15.796 m/s²</em>
Answer: (b)
Explanation:
Given
Mass of box 
Applied force 
Friction force 
Box travels a distance of 
time taken 
Net unbalanced force 
Work done by the unbalanced force

Power developed by unbalanced force

Thus, option (b) is correct.
Formulas you need for this problem:
F= mass•acceleration
KE= mass•velocity^/2
Acceleration= final velocity-intial velocity/time
time= distance/speed
t= 97.5\10= 9.75 seconds
Acc= 10-20/9.75= -1.03 m/s/s
These are the answers :)
F=650•-1.03= -669.5N
KE= 650•100/2= 32,500J or 32.5KJ