It is more difficult to start moving a heavy carton from rest than it is to keep pushing it with constant velocity. This is because: a. the normal force (N) is greater when the carton is at rest.
b. the coefficient of static friction is less than the coefficient of kinetic friction.
c. initially, the normal force (N) is not perpendicular to the applied force.
d. the coefficient of static friction is greater than the coefficient of kinetic friction.

d. the coefficient of static friction is greater than the coefficient of kinetic friction.

Explanation:

The magnitude of the for required to be applied to the carton is given as equal to the frictional force of between the carton and the surface. So, when the carton is at rest:

F = μs*W

and when the carton is in motion:

F = μk*W

where,

F = Force Required

μs = coefficient of static friction

μk = coefficient of kinetic friction

W = Weight of Carton

Since, the weight is constant. Therefore, for the increase in the force required to move the carton at rest than the force required to keep pushing the carton in velocity, the coefficient of static friction must be greater than the coefficient of kinetic friction. Therefore, the correct option is:

d. the coefficient of static friction is greater than the coefficient of kinetic friction.

yup its correct its: c) b b