## Hovercraft B/C

Zioly
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Posts: 152
Joined: April 17th, 2016, 4:50 pm
Division: B
State: WA

### Re: Hovercraft B/C

So close
Sorry about that, but wouldn't it be N/s? Also, what unit is momentum in? I had a question on a test the other day and was uncertain... as you can tell, impulse and momentum are concepts I'm not as familiar with.
No, it's N*s. As you said, the unit of momentum is kg*m/s. Since Impulse is the change in momentum, it will have the same unit. A Newton is kg*m/s^2. Therefore, the unit for momentum is the Newton times a unit of time.
Oooohh, I didn't realize that a Newton is how much a kilo can be accelerated! Thanks for the tip!
2017 Nats Div. B
Inglemoor High School 2018 Div. C

Member
Posts: 81
Joined: January 14th, 2016, 4:53 pm
Division: C
State: PA

### Re: Hovercraft B/C

Sorry about that, but wouldn't it be N/s? Also, what unit is momentum in? I had a question on a test the other day and was uncertain... as you can tell, impulse and momentum are concepts I'm not as familiar with.
No, it's N*s. As you said, the unit of momentum is kg*m/s. Since Impulse is the change in momentum, it will have the same unit. A Newton is kg*m/s^2. Therefore, the unit for momentum is the Newton times a unit of time.
Oooohh, I didn't realize that a Newton is how much a kilo can be accelerated! Thanks for the tip!
Yup, right from F=ma

Zioly
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Posts: 152
Joined: April 17th, 2016, 4:50 pm
Division: B
State: WA

### Re: Hovercraft B/C

Sorry, I thought that since I got it wrong, someone else could have a go at the right answer and put up the next question.

You drop a ball from a 26 meter tall building on earth. Find the velocity when the ball hit the ground. Assume no air resistance and gravity as 9.81. Show all work.
2017 Nats Div. B
Inglemoor High School 2018 Div. C

RestingDoll
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Posts: 34
Joined: September 14th, 2016, 5:10 am
Division: C
State: PA

### Re: Hovercraft B/C

Sorry, I thought that since I got it wrong, someone else could have a go at the right answer and put up the next question.

You drop a ball from a 26 meter tall building on earth. Find the velocity when the ball hit the ground. Assume no air resistance and gravity as 9.81. Show all work.
v^2=vi^2+2a(delta_y)
v^2=0-2g(26)
v^2=510.12
v=22.5858 m --> v~23 m
Last edited by RestingDoll on March 13th, 2017, 7:47 pm, edited 1 time in total.

RestingDoll
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Posts: 34
Joined: September 14th, 2016, 5:10 am
Division: C
State: PA

### Re: Hovercraft B/C

Sorry, I thought that since I got it wrong, someone else could have a go at the right answer and put up the next question.

You drop a ball from a 26 meter tall building on earth. Find the velocity when the ball hit the ground. Assume no air resistance and gravity as 9.81. Show all work.
Wait lol how do I hide it. Edit: nvm, figured it out

Zioly
Member
Posts: 152
Joined: April 17th, 2016, 4:50 pm
Division: B
State: WA

### Re: Hovercraft B/C

Sorry, I thought that since I got it wrong, someone else could have a go at the right answer and put up the next question.

You drop a ball from a 26 meter tall building on earth. Find the velocity when the ball hit the ground. Assume no air resistance and gravity as 9.81. Show all work.
v^2=vi^2+2a(delta_y)
v^2=0-2g(26)
v^2=510.12
v=22.5858 m --> v~23 m
All correct, except for that one little misclick. (You typed "-" instead of "+" in line 2. Your go!)
2017 Nats Div. B
Inglemoor High School 2018 Div. C

RestingDoll
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Posts: 34
Joined: September 14th, 2016, 5:10 am
Division: C
State: PA

### Re: Hovercraft B/C

A small 60 g point mass starts sliding down a frictionless surface at 30 cm in height, then sticks to the end of a uniform rod of mass 120 g and length 40 cm. The rod rotates about a point "O" lengthwise and its moment of inertia about that point is given by 1/3 mr^2. After the point mass sticks to the rod, it pivots to an angle theta, before momentarily stopping. Find theta. (Hint: Don't forget that the potential energy stored after it pivots is based on the center of mass of the entire system.)

Tom_MS
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Posts: 41
Joined: April 28th, 2015, 11:08 am
State: PA

### Re: Hovercraft B/C

A small 60 g point mass starts sliding down a frictionless surface at 30 cm in height, then sticks to the end of a uniform rod of mass 120 g and length 40 cm. The rod rotates about a point "O" lengthwise and its moment of inertia about that point is given by 1/3 mr^2. After the point mass sticks to the rod, it pivots to an angle theta, before momentarily stopping. Find theta. (Hint: Don't forget that the potential energy stored after it pivots is based on the center of mass of the entire system.)
I'm getting

RestingDoll
Member
Posts: 34
Joined: September 14th, 2016, 5:10 am
Division: C
State: PA

### Re: Hovercraft B/C

A small 60 g point mass starts sliding down a frictionless surface at 30 cm in height, then sticks to the end of a uniform rod of mass 120 g and length 40 cm. The rod rotates about a point "O" lengthwise and its moment of inertia about that point is given by 1/3 mr^2. After the point mass sticks to the rod, it pivots to an angle theta, before momentarily stopping. Find theta. (Hint: Don't forget that the potential energy stored after it pivots is based on the center of mass of the entire system.)
I'm getting
Interesting... I think you may be forgetting that the center of mass of the system is different than the center of mass of the rod.