3. The brakes on a 20 kg cart are locked so that the rubber wheels cannot turn. A child
pushes horizontally to the right on the cart until it just begins to slide. The maximum
horizontal force he applies is 150,N. After that the child is able to keep the cart sliding
with a horizontal force of 80 N.
3.1 Define a normal force.
3.2 Explain the difference between static and kinetic friction.
3.3 Calculate the coefficients of static and kinetic friction between the rubber wheels
and the ground

(2)
(2)
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