[ 3 / biz / cgl / ck / diy / fa / ic / jp / lit / sci / vr / vt ] [ index / top / reports ] [ become a patron ] [ status ]
2023-11: Warosu is now out of extended maintenance.

/sci/ - Science & Math

View post   
File: 10 KB, 220x293, 220px-Albert_Einstein_1947.jpg [View same] [iqdb] [saucenao] [google]
5208113 No.5208113 [Reply] [Original]

2. A 1.0 kg wood block is on the edge of a table, which top is 1.0 m above the ground. A 15 g bullet strikes and lodges into the block. The block lands on the ground 0.75 m from the edge of the table.
What was the bullet’s velocity when it struck the bock? Assume no loss of energy.


What the hell is going on here?!

>> No.5208124

Need physics help bump

>> No.5208137

Can anyone help?

>> No.5208145

We really need those derivative Captchas

>> No.5208147

>>5208145
Is it possible to derive something to take the derivative of in this?

>> No.5208156

Bump

>> No.5208175

>homework

>> No.5208178

Sounds like it's just an elastic collision. Use conservation of momentum and of kinetic energy and you're half-way there.

>> No.5208180

>Assume no loss of energy.

Impossible. The block starts at table height, and ends up motionless on the floor . Some energy must have been dissipated.

>> No.5208182

work backwards, use the basic equations of motion, and then conservation of momentum.

>> No.5208183

>>5208178
>A 15 g bullet strikes and lodges into the block.
>Sounds like it's just an elastic collision.
wat

>> No.5208187

>>5208183
Sorry, wasn't reading very well, the "no loss of energy" made me think it was elastic. (It should be no loss of kinetic energy for that, I know, I'm a bit sleepy).

>> No.5208195

Okay try this. Find the velocity it takes for the block to fall down so that you can find the time. (vy^2)=Vyi + 2a(-xi) which will give (vy^2)=2*9.8*(1-0) which is (vy^2)=19.6 then (vy)~4.427. Now find the time,vy=vyi+at, then solve for t, t=vy/a, 4.427/9.8=.452 sec. Now we find the velocity of the x component since we now have t time and the given dist of .75m, vx=dist/t, vx+.75/.452~1.659. Now that we have the mass of the block (1kg) and the bullet (.015kg) and the velocity of the block (1.659) we can use the equation m1v1=m2v2 which is (1)(1.659)=(.015)(v2). Just divide the left side by (.015) and you should set.

>> No.5208210

>>5208187
that part is just wrong. energy isnt conserved in an inelastic collision.

>> No.5208231

>>5208210

but you can calculate the speed of the block as it leaves the table, and thus the momemtum and speed of the bullet.

everything is assumed to be ideal, frictionless, elastic, etc, except the bullet imbeds in the block and the two now have all the kinetic energy, which is lost when it hits the groound, but that is beside the point.

>> No.5208238

>>5208231
no, momentum is conserved. kinetic energy is not.

>> No.5208456
File: 293 KB, 1276x1656, IMG.jpg [View same] [iqdb] [saucenao] [google]
5208456

>> No.5208497
File: 18 KB, 814x503, solution.png [View same] [iqdb] [saucenao] [google]
5208497

did it pretty quick so I may have done a mistake somewhere, but it is the right method

>> No.5208507

>>5208180
Physics problems, always presume a vaccuum and a perfect resistanceless environment. All energy is conserved but not lost to surrounding environment

>> No.5208508

>>5208497
>>5208456
interesting, a 10m/s difference

I wasn't bothering to conserve decimals though, so top one is likely more accurate

>> No.5208511
File: 20 KB, 250x250, 1327687058754.jpg [View same] [iqdb] [saucenao] [google]
5208511

>>5208497
>QED
MUH NIGGUH

>> No.5208541

first figure out how long it took the 1.015 kg block to fall 1 m based on g=9.81 m/s^2. then, find the velocity using said time of fall and distance of 0.75 m. multiply by 1.015 kg to obtain momentum. divide by .015 kg, mass of buller, to find velocity of bullet. voila.

>> No.5208543

>>5208508
>>5208497
yeah. you forgot to add the mass of the bullet to the mass of the block. it was an inelastic collision.

>> No.5208564

If air resistance is neglected, the horizontal component of its velocity remains constant. There is also no vertical component when the bullet strikes the block.

>> No.5208600

>>5208543
ah indeed
I overlooked that

>> No.5208608
File: 117 KB, 267x400, Sadness.png [View same] [iqdb] [saucenao] [google]
5208608

This isn't a hard problem people!

>> No.5208616

What's a bock?

>> No.5208612

Inelastic collision
Conservation of energy
If you can't solve this you shouldn't be on /sci/

>> No.5208693

>>5208612
>can't into physics
>shouldn't be on /sci/

>> No.5208705

I'm so sick of retards posting Einstein as if he was the greatest genius of all times. He's a fucking pop sci faggot. His theory of relativity isn't impressive at all and can be understood by any highschooler. Einstein failed at babby tier math and his quotes on philosophy are nothing but uneducated drivel. Stop worshipping this guy and do some real fucking science.

>> No.5208708

>>5208705
>His theory of relativity
Neither special nor general relativity was invented by him.

>> No.5208723

>>5208708
Even more reason to ignore that faggot.

>> No.5208732

>>5208705
+1

pretty sure its christian trolls that always post him or similar plebs

>> No.5208742

>>5208705
While I agree on the shit-tier quality of his quotes, he's definitely done more than the theory of relativity which is worth mentioning.

>> No.5208760

>>5208180
You could stretch the meaning of "lands" to "touches and continues to bounce and roll forever" I guess.

>> No.5208765

>>5208497
>QED
>what was to be shown

You didn't show anything. You gave an answer to a question.

>> No.5208829

>>5208497
QED only makes sense for proofs

>> No.5208880

>>5208829

it's latin for "quickly ends discussion", so it is appropirate in that case as well.

>> No.5208926

>>5208880
I thought it was Latin for Little White Box.