Author Topic: Physics momentum Question help please  (Read 3169 times)

Offline helai.j

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Physics momentum Question help please
« on: October 09, 2010, 12:51:41 pm »
No one seams to answer my Questions when i post in the specific topics so, i guess no harm trying here :)

can anyone answer these 2 Questions for me please ? i dont need just the answers i want to know how they are done . thanks

1)   A movie stuntman with a mass of 90 kg stands on a stationary 1 kg skateboard. An actor shoots the stuntman with a 9 mm pistol. The 8-gram bullet leaves the pistol at 358 m s?1 and embeds completely in the stuntman’s bulletproof vest. At what speed will the stuntman roll away?


2)   In a stunt for an action movie, the 100 kg actor jumps from a train which is crossing a river bridge. On the river below, the heroine is tied to a raft floating towards a waterfall at 3 m s?1. The raft and heroine have a total mass of 200 kg.

a    If the hero times his jumps perfectly so as to land on the raft, and his velocity is 12 m s?1 at an angle of 80° to the river current, what will be the velocity of the raft immediately after he lands? Draw a vector diagram to show the momentum addition. (Ignore any vertical motion.)

b    If the waterfall is 100 m downstream, and the hero landed when the raft was 16 m from the bank, would they plummet over the fall? (Assume the velocity remains constant after the hero has landed.)



i would love to have a studying friend who studies A2 chem,bio, phy. work out problems together and so on.

Offline ashish

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Re: Physics momentum Question help please
« Reply #1 on: October 09, 2010, 02:59:11 pm »


1)   A movie stuntman with a mass of 90 kg stands on a stationary 1 kg skateboard. An actor shoots the stuntman with a 9 mm pistol. The 8-gram bullet leaves the pistol at 358 m s?1 and embeds completely in the stuntman’s bulletproof vest. At what speed will the stuntman roll away?




since momentum is always conserved

(8/1000)*358=(90+1)*V
V=0.03147m/s 

i find this speed weird !
is it right?

Offline helai.j

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Re: Physics momentum Question help please
« Reply #2 on: October 09, 2010, 04:14:52 pm »
yes that one is correct, thank you :)



i would love to have a studying friend who studies A2 chem,bio, phy. work out problems together and so on.

Offline ashish

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Re: Physics momentum Question help please
« Reply #3 on: October 09, 2010, 04:17:51 pm »
yes that one is correct, thank you :)
:D you are welcome

nid404

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Re: Physics momentum Question help please
« Reply #4 on: October 10, 2010, 09:37:36 am »
2)   In a stunt for an action movie, the 100 kg actor jumps from a train which is crossing a river bridge. On the river below, the heroine is tied to a raft floating towards a waterfall at 3 m s?1. The raft and heroine have a total mass of 200 kg.

a    If the hero times his jumps perfectly so as to land on the raft, and his velocity is 12 m s?1 at an angle of 80° to the river current, what will be the velocity of the raft immediately after he lands? Draw a vector diagram to show the momentum addition. (Ignore any vertical motion.)

b    If the waterfall is 100 m downstream, and the hero landed when the raft was 16 m from the bank, would they plummet over the fall? (Assume the velocity remains constant after the hero has landed.)

I was looking for astar's post but failed. I tried, I'm not sure but this took me 15 mins only to figure out the entire scene  ::)  :P

a) So perependicular to river's flow. Y component velocity

100X 12sin80+ 200X0= (100+200)v
v=3.94m/s
^^speed to the bank...sidestream
Parallel to river's flow. X component of velocity

100X12cos80+ 200X3= (100+200)v
v= 2.69m/s
^^speed to the waterfall...downstream
b) Time taken to reach the bank= 16/3.94 = approx 4s
    Time taken to reach the falls= 100/2.69=approx 37s

the raft will this reach the bank safely.

I'm not sure. -.-

Offline Deadly_king

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Re: Physics momentum Question help please
« Reply #5 on: October 10, 2010, 10:31:47 am »
I was looking for astar's post but failed. I tried, I'm not sure but this took me 15 mins only to figure out the entire scene  ::)  :P

a) So perependicular to river's flow. Y component velocity

100X 12sin80+ 200X0= (100+200)v
v=3.94m/s
^^speed to the bank...sidestream
Parallel to river's flow. X component of velocity

100X12cos80+ 200X3= (100+200)v
v= 2.69m/s
^^speed to the waterfall...downstream
b) Time taken to reach the bank= 16/3.94 = approx 4s
    Time taken to reach the falls= 100/2.69=approx 37s

the raft will this reach the bank safely.

I'm not sure. -.-

Well.....it seems good to me :)

The last answer was obvious. Hero and heroine always comes out alive :P

nid404

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Re: Physics momentum Question help please
« Reply #6 on: October 10, 2010, 10:34:20 am »
Well.....it seems good to me :)

The last answer was obvious. Hero and heroine always comes out alive :P

Looks good...seems good....i...don't...know...if...it....actually...is....the....right....answer :P

HAHAHA.....If it's a bollywood movie...then we can be 100% sure  :P

Offline Deadly_king

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Re: Physics momentum Question help please
« Reply #7 on: October 10, 2010, 10:43:18 am »
Looks good...seems good....i...don't...know...if...it....actually...is....the....right....answer :P

HAHAHA.....If it's a bollywood movie...then we can be 100% sure  :P

Hehe.....don't worry we'll get to know that soon.
If it is the right answer.......then hats off to you :)
If it is not.......then we'll have to find another way to get it ;)

Yeah.........  :D

Offline helai.j

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Re: Physics momentum Question help please
« Reply #8 on: October 11, 2010, 03:24:05 pm »
the b part is correct but A isnt, that answer is attached bellow



i would love to have a studying friend who studies A2 chem,bio, phy. work out problems together and so on.

elemis

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Re: Physics momentum Question help please
« Reply #9 on: October 11, 2010, 03:30:20 pm »
the b part is correct but A isnt, that answer is attached bellow
LoLzzz  ;D

nid404

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Re: Physics momentum Question help please
« Reply #10 on: October 11, 2010, 03:33:12 pm »

Offline S.M.A.T

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Re: Physics momentum Question help please
« Reply #11 on: October 11, 2010, 04:10:51 pm »
here


"A man's life is interesting primarily when he has failed - I well know. For it's a sign that he tried to surpass himself." Clemenceau, Georges

Offline helai.j

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Re: Physics momentum Question help please
« Reply #12 on: October 11, 2010, 08:36:42 pm »
haha i didnt notice wat i attached ! LOL sorry guys  here it is



i would love to have a studying friend who studies A2 chem,bio, phy. work out problems together and so on.

Offline Deadly_king

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Re: Physics momentum Question help please
« Reply #13 on: October 12, 2010, 05:35:47 am »
here

Big thanks to the member of the month :D