a) E = Ep = m*g*h = 2*10*4 = 80 J
b) Lf= -μ*N*d
Ff=μ*N=μ*Gn=μ*m*g*cosα
d=h*sinα= 2√2 m
Lf= -μ* m*g*cosα *d= - 0.3 * 2 * 10 * 1/2 = -3 J
c)N=Gn=Gcosα
G=m*g
Gtg - Ff = m*a
m*g*sinα - μ*m*g*cosα=m*a ⇒
a = g*sinα - μ*g*cosα = 10*√3/2 - 0.3*10*1/2
a = 2√2 - 3/2 m/s² sau a=1.32 m/s²