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[jaunty kayak]

Keeping in mind Ff = uN where Ff is force of friction, u is coefficient of friction and N natural force...

Then just a matter of keeping component acceleration straight in relation to impacts downward and therefore N acting back up

in Case 1, the imparted P force only acting with an acceleration in the x direction (horizontal), so it's not applying any extra acceleration downward... so the only ay acceleration is gravity, so N = mg ... therefore Ff = u(mg)

In case 2, the P force is angled downward, so you need to resolve it's component forces into Px and Py, and add that Py to mg (mass x gravity) to determine N and thus Ff

Case 3 is opposite case 2, where P is acting upward, such that it's Py acceleration is subtracted from mg to find N and thus Ff