Physics homework?

Question

Please explain to me how these problems are solved,I have noooo clue!

1) a baseball player slides into third base with an initial speed of 7.90 m/s. if the coefficient of kinetic friction between the player and the fround is .41, how far does the player slide before coming to rest?

2)a child does down a playground slide with an acceleration of 1.05 m/s2. find the coefficient of kinetic friction between the child and the slide if the slide is inclined at an angle of 35degrees below the horizontal.

3)hopping into your Porsche, you floor it and accelerate at 12m/s without spinning the tires. determine the minimum coefficient of static friction between the tires and the road needed to make this possible.

4)when you push a 180-kg book resting on a tabletop,it takes 2.25 N to start the book sliding.once it is sliding, however,it takes only 1.50N to keep the book moving with constant speed. what are the coefficients of static and kinetic friction between the book and the tabletop?

Answer 1

1) Using energy
.5*m*7.9^2=m*g*0.41*d
solve for d. g=9.8

d=7.8 m

2) Consider a FBD of the child
m*g*sin(35)-m*g*cos(35)*u=
m*1.05
solve for u, g=9.8

u=(g*sin(35)-1.05)/(g*cos(35))
u=0.57

3) is that 12 m/s^2?
m*12=m*g*u
solve for u - this requires u>1
u=12/g

4) 180*9.8*us=2.25
us=2.25/(180*9.81)

uk=1.5/(180*9.81)


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