Physics Questions - please help - do not understand what they are asking?

Question

I found the first part.

Please read the question:

A block of mass 15 kg starts from rest and slides a distance of 6 m down an inclined plane making an angle of 40 degrees with the horizontal. The coefficient of sliding friction between block and plane is 0.4 .
The acceleration of gravity is 9.8 m/s^2.

Question one - What is the net force on the block along the incline? answer in units on N.

Answer - I know the answer to question one is 49.446365.

HERE IS THE HELP I NEED

QUESTION 2 - What is the speed of the block after sliding 6 meters? Answer in units of m/s.

QUESTION 3 - What would be its speed if friction were negligible? Answer in units of m/s.

APPRECIATE EVERYONES HELP!!!!!

THANK YOU!!!!

Answer 1

The net force is
m*g*sin(40)-m*g*cos(40)*0.4

49.45 correct

There are two ways to solve this.

since we know the acceleration, we can use
s(t)=.5*a*t^2
and solve for t, which we plug into
v(t)=a*t

solver for a
49.45=15*a
a=3.3 m/s^2

when s=6m, t is
6=.5*3.3*t^2
t=1.91 sec

v(1.91)=3.3*1.91
v=6.29 m/s

Another way to solve it is using energy
m*g*h-f*d=.5*m*v^2
v=sqrt(2*g*h-2*f*d/m)
h=6*sin(40)
f/m=g*cos(40)*.4

v=6.29 m/s

it checks

without friction, using energy
v=sqrt(2*g*h)
v=8.69 m/s

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