How fast would you have to throw a 150-g rock for it to have t...

Question

How fast would you have to throw a 150-g rock for it to have the same momentum as a 10-g sniper rifle bullet traveling at 900 m/s?

Accepted Answer

Hey guys, let's check out this practice problem here. So we have to figure out how fast we have to throw a 150 g rocks, that has the same momentum as a speeding bullet. So here, I've got the mass of the rock is uh it's 150 g. So that's actually 0.15 kg. And I want to do is I want to figure out the speed of this rock here. I know the mass of the bullet, on the other hand is 10 g. So this is gonna be 0.1 kg. And the speed of this bullet here is gonna be 900. So what happens is I have this rock like this and I want to throw this rock with some speed. This is my VR that I'm actually looking for. Such that it has the same momentum as the speeding bullet here, which is traveling very, very, very fast. We know this VB is equal to 900. So, how do we do this? We'll remember that the product of mass and speed, right? M times V is gonna give you the momentum, right? So, these two are gonna give the momentum of the rock. This pr and this is gonna give you the momentum of the bullets in order for them to be the same. We're just gonna set these two things equal to each other. So, really, what happens is that P. R. Is equal to P. B. That's what we want. So that means that the mass times the speed of r is equal to the mass times the speed of B. Now we have three to the four variables, we just have to go ahead and solve for VR. So I have 0.15 V. R. Equals 0.1 times the speed of B, which is um 900. So we can work this out. You're gonna get is that VR is equal to um nine divided by 0.15. And it's gonna give you 60 m per second. So you would have to throw this rock at 60 m per second, which is almost like 100 and 30 miles an hour for it to have the same momentum as the speeding bullet here. So that just goes to show how much momentum this 10 g bullet has, even though it has a mass, it's very very very small. This 900 m per second means it has a very very high momentum and it's very difficult to stop. Alright, so that's it for this one. Guys, let me know if you have any questions

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