A shopper pushes a grocery cart for a distance 18 m at constant speed on level g

Question

A shopper pushes a grocery cart for a distance 18 m at constant speed on level ground, against a 42.5 N frictional force. He pushes in a direction 25 degree below the horizontal. What is the work done on the cart by friction, in joules? What is the work done on the cart by the gravitational force, in Joules? What is the work done on the cart by the shopper, in joules? Find the magnitude of the force, in newtons, that the shopper exerts on the cart. What is the total work done on the cart, in Joules?

Explanation / Answer

a) W_friction = Ff*d*cos(180)

= 42.5*18*cos(180)

= -765 J

b) W_gravity = Fg*d*cos(90)

= 0

c) W_shopper = -W_friction

= -(-765)

= 765 J

d) W_shopper = F_shopper*d*cos(25)

F_shopper = W_shopper/(d*cos(25)

= 765/(18*cos(25))

= 46.9

e) Wnet = 0

because there in no change in kinetic energy.

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