Crates a and b sit at rest side by side on a frictionless...

Crates A and B sit at rest side by side on a frictionless horizontal surface. They have masses ma and mb, respectively. When a horizontal force F is applied t o crate A, the two crates move off to the right. (a) Draw clearly labeled free-body diagrams for crate A and for crate B. Indicate which pairs of forces, if any, and third-law action-reaction pairs. (b) If the magnitude of F is less than the total weight of the two crates, will it cause the crates to move? Explain.

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Transcript

00:03 Okay, we have two crates that are side by side on a frictionless surface.

00:13 They have masses of m .a.

00:19 And m .b respectively.

00:24 And there's a force applied to the crate on the left, and then the two crates move to the right.

00:33 Okay.

00:36 So we're asked to draw everybody to diagrams for the crates.

00:44 So let's do that first.

00:49 So we want to do a free body diagram.

00:52 So let's look at crate a first of all.

00:55 We'll represent it by this dot.

00:56 We have a normal force.

01:00 I'll write it normal sub a.

01:03 And we have the gravitational force on a.

01:11 And then we have the applied force.

01:15 I'll just call that f and then a is touching b so that means b is pushing back on a so we'll call this the force on a by b okay and then we could also write the frictional force here if we really wanted to pushing the block to the left but it does say it's frictionless so i think in this case, we'll just leave friction out, because the force is zero.

01:50 So there's a.

01:52 Here's the force on, or the forces on b.

01:54 We have the normal force, the gravitational force.

02:02 And then we have the force of a, the force on b by a.

02:12 So that's what's pushing block b.

02:14 And then no friction as well...