a contestsant in a winter games event pushes a 32.0 -kg rock across a frozen lak

Question

a contestsant in a winter games event pushes a 32.0 -kg rock across a frozen lake with a force of 25 N at 22 degree below the horizontal as showin in figure (a) below and it moves wirth an acceleration of .72 m/s^2 to the right.

a)waht is the normal force exerted by the lake surface on the rock?

b)instead of pushing on nthe rock, the conrestant now pulls on it with a rope over his shoulder at the same angle above the horizontal as in part (a). see figure (b) above. now what is the normal force exerted by the lake surface on the rock?

Explanation / Answer

a)

horzizantal component of force exerted = Fx

Fx = F*cos22 = 25*cos22

vertical component = Fy = -F*sin22 = -25*sin22

gravitational force Fg = -m*g

the normal force acing = N

in equilibrium along vertical

N + Fg + Fy = 0

N = mg + F*sin22

N = (32*9.8)+(25*sin22)

N = 323 N <<<<----------answer

(b)

Fx = F*cos22

Fy = +F*sin22 = +25*sin22

Fg = -m*g

N + Fy + Fg = 0

N = m*g - Fy

N = (32*9.8)-(25*sin22)

N = 304.23 N   <<<-----answer

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