Required information a 5013 lb truck is being used to lift a...

Required information A 5,013-lb truck is being used to lift a 1,013-lb boulder B that is on a 330-lb pallet A. The acceleration of the truck is $1 \text{ ft/s}^2$ and $g = 32.2 \text{ ft/s}^2$. a B A Determine the horizontal force between the tires and the ground. The horizontal friction force between the tires and the ground is $\text{lb}$.

Transcript

00:01 In this problem, we have a truck that's lifting this boulder that's resting on a platform here.

00:10 And so we have the configuration here.

00:13 I'll try to sketch it a little bit better here.

00:15 So we have this cable and we have it coming up over another pulley.

00:20 And so there's a pulley here that's then fixed to ground here.

00:26 And so this is attached to the truck.

00:29 So we have basically this mechanical.

00:31 Advantage of wrapping this cable around this pulley and then this is attached to the boulder and this is obviously fixed.

00:39 Obviously it's shown in the book in the figure.

00:43 So what we need to do is if we take a look at the free body diagram of this pulley here.

00:50 Now we're assuming this pulley doesn't have any mass or at least there's negligible mass compared to the platform and the boulder.

00:57 We see that we get if we cut, we isolate it.

01:01 So we isolate it.

01:03 So we have a tension in the cable over here.

01:06 We have the same tension in the cable over here because it's the same cable being wrapped around.

01:11 And then we have the force from the from the cable attached to the center that's attached to the platform.

01:19 So that tells us that 2t minus f equals zero.

01:22 And again, because we assume that the mass of this was negligible.

01:26 We also know just from kinematics that this is kind of like a wheel rolling.

01:31 So at any, the instant this point is fixed this point is accelerating with an amount of the same as the truck which means that this point in the center is accelerating with half that amount so the acceleration of this pulley is half the acceleration of the truck and the acceleration of the truck was given as one meters per second squared so acceleration the pulley is moving up at um half a meter per second squared uh with an acceleration um and again we assume the mass was zero but so so that doesn't come into account here, but it does come into account because the boulder is also moving up at that rate.

02:09 So if we look at the boulder, again, we've cut the cable from the pulley here.

02:15 And then we just have the force from it.

02:18 And then we have the weight of the boulder plus the platform.

02:21 And then it is also accelerating...

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