Two crates are stacked on top of each other on a horizontal floor, crate #1 is on the bottom, and crate #2 is on the top. Both crates have the same mass. Compared with the strength of the force F_(1) necessary to push only crate #1 at a constant speed across the floor, the strength of the force F_(2) necessary to push the stack at the same constant speed across the floor is greater because

Two crates are stacked on top of each other on a horizontal floor, cra

1.	Two crates are stacked on top of each other on a horizontal floor, crate #1 is on the bottom, and crate #2 is on the top. Both crates have the same mass. Compared with the strength of the force F_(1) necessary to push only crate #1 at a constant speed across the floor, the strength of the force F_(2) necessary to push the stack at the same constant speed across the floor is greater because
Answer» the FORCE of the floor on crate #1 is greater because of the additional weight being SUPPLIED by crate #2 the coefficient of kinetic friction between crate #1 and the floor is greater the force of kinetic friction, but not the NORMAL force, on crate #1 is greater the coefficient of static friction between crate #1 and the floor is greater Solution :With crate #2 on top of crate #1, the force pushing downward on the floor is greater, so the normal force exerted by the floor on crate #1 is greater, which increases the friction force. Choices (B), (C ) and (D) are all FALSE.

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