“Yes, sir.”
But Maya was stubborn. She wanted to learn , not copy. “Yes, sir
“A 200-kg crate rests on a rough inclined plane… determine the smallest horizontal force P required to push it up the incline.” She’d drawn four free-body diagrams. Friction pointed the wrong way in three of them. In the fourth, she forgot the normal force entirely. Friction pointed the wrong way in three of them
Here’s a short story based on your request. The Crate on the Incline The Crate on the Incline Maya’s hand shot up
Maya’s hand shot up.
By 1:30 a.m., she’d solved it — or thought she had. But when she checked her answer against the back of the book ( P = 1.27 kN ), she got 1.52 kN. Off by nearly 20%.
Page 8-25. There it was: a clean free-body diagram with the friction vector down the plane (she’d put it up — wrong assumption), and the normal force correctly split into components. Step by step, Hibbeler’s method revealed her mistake: she’d used the wrong friction direction because she’d forgotten that impending motion up means friction acts down .