By how much does the gravitational potential energy increase during the block's motion?

Question

A 5.0 kg block is pushed 2.0 m up a vertical wall with constant speed by a constant force of magnitude F applied at an angle of = 30° with the horizontal, as shown in Figure P5.70. If the coefficient of kinetic friction between block and wall is 0.30, determine the work done by each of the following.

Figure P5.70 http://www.webassign.net/sf/p5_70.gif


(a) the force
J
(b) gravity
J
(c) the normal force between block and wall
J
(d) By how much does the gravitational potential energy increase during the block's motion?
J

Answer 1

a) The work done by F is F*sin(30)*2

or F*1
But what is the force?
friction is
F*cos(30)*0.3
so F*(sin(30)-cos(30)*.3)=
5*9.8
F=204 N

so the work is
204 J

b) Gravity is -m*g*h or
=-5*9.8*2=-98
c) The formal force does zero


d) The gain in PE is m*g*h, or 5*9.8*2
98 J

check
204*cos(30)*.3*2
106

add 98 and
you get 204 J

yes, it checks.

j