00:01
Okay, so we've got a block.
00:09
Draw it here.
00:11
I'm going to call it m1, and it's going to sit on another block, m2, which sits on a table.
00:23
We've got m1 is 5 kilograms, m2 is 15 kilograms, and then mu, and then mu, between the blocks, static, is this.
00:56
Mew between the blocks, kinetic is this.
01:04
Actually, that first one should have been a three.
01:13
Mew with the table static is this.
01:20
Mew table kinetic is this.
01:31
A.
01:33
Body diagram of each block naming the forces.
01:47
There's going to be, oh wait, i forgot the force f here.
01:55
Okay, m1, there's going to be the weight, gravitational force, there's going to be the normal force, and then there's going to be a frictional force that's going to cause that block to move in this direction.
02:29
Okay.
02:31
Now, in block number two, there's going to be gravitational force.
02:43
There's also going to be fg1 from above.
02:57
There's also going to be a normal force.
03:05
There's also going to be a frictional force from above, and then there's going to be a frictional force with the table.
03:24
Okay.
03:25
Now, i did notice that the answers are in the back of the book.
03:30
So i see a normal force on one, friction on one, and weight on one.
03:36
Very good.
03:38
One, two.
03:40
I see friction.
03:43
Two frictions.
03:45
Oh, i forgot to put the main force, the pushing force.
03:54
Yep.
03:54
Okay, i've got all of them labeled.
03:57
Now, next part of the question is just before it moves, at the instant when you've started.
04:19
Pushing, but we haven't quite started to move yet.
04:27
So in b, fg1 is just going to be m1 times g.
04:39
Fg2 is going to be m2 times g.
04:41
So fn1 is going to be m2 times g.
04:49
So fn1 is going to be fg1.
04:53
So they oppose each other.
04:59
Fn2 is going to be fg2 plus fg1.
05:13
Okay, so let's make sure that i get those, putting this in a calculator.
05:19
M1 is 5, m2 is 15, mu b, s is 3, mu b k, and is 0 .1, that should have been 0 .3.
05:50
Okay.
05:53
Mu t .s is 0 .5.
06:10
Mut k is .4.
06:21
G is 9 .81.
06:25
Okay.
06:27
Now, let's get some of these.
06:30
M1g.
06:34
So fg1 is m1g that's 49 .1.
06:53
Fg2 is m2g 147 fn2 equals fg1 plus fg2 199 so let's make sure that i got these right.
07:51
49 .1, 147, 196.
07:59
196, 496, 496, 49 .1, 147.
08:05
Okay, very good.
08:07
I've got the vertical ones correct.
08:10
Now, horizontal ones, ffb looks easy, is just going to be, for, of friction in the b direction.
08:59
Well, that's going to equal m1 times a1.
09:15
Let me look at the question again.
09:24
If no motion has started, if m1 is not accelerating at all, then ffb would have to be zero because it equals m1, times acceleration.
10:05
Fft would have to oppose f.
10:13
F.
10:16
F f t minus f would have to be zero.
10:23
So fft would be fft, which would be mu sub s times the normal force on two.
10:47
But the normal force on 2 is fn2...