Help with 3 Physics problems
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From: Androcles on 30 Sep 2007 16:36 <shreemayeede(a)gmail.com> wrote in message news:1191179769.958384.218990(a)d55g2000hsg.googlegroups.com... On Sep 30, 10:30 am, John C. Polasek <jpola...(a)cfl.rr.com> wrote: > On Sun, 30 Sep 2007 04:57:39 -0000, shreemaye...(a)gmail.com wrote: > >I need hep with these three problems: > > >1) A block is hung by a string from the inside roof of a van. When > >the van goes straight ahead at a speed of 23 m/s, the block hangs > >vertically down. But when the van maintains this same speed around an > >unbanked curve (radius = 150 m), the block swings toward the outside > >of the curve. Then the string makes an angle theta with the vertical. > >Find theta. > > >2) Your baggage is on a carousel at an airport. Your suitcase has not > >slid all the way down the slope and is going around at a constant > >speed on a circle (r = 12.6 m) as the carousel turns. The coefficient > >of static friction between the suitcase and the carousel is 0.760, and > >the angle that the baggage on the carousel makes with the horizontal > >plane is 36.0�. How much time is required for your suitcase to go > >around once? > > >3) In an automatic clothes drier, a hollow cylinder moves the clothes > >on a vertical circle (radius r = 0.39 m). The appliance is designed so > >that the clothes tumble gently as they dry. This means that when a > >piece of clothing reaches an angle of above the horizontal, it loses > >contact with the wall of the cylinder and falls onto the clothes > >below. How many revolutions per second should the cylinder make in > >order that the clothes lose contact with the wall when theta = 72.0�? > > >Thank you very much for your help. > > As a start draw some vector diagrams. You should be able to label some > of the legs with forces. If you can't solve them from these figures, > you can't solve them with algebra either. > John Polasek The post that told me to read my book or to pay attention in lecture, I have done so. I have drawn vector diagrams, I have tried a lot of different techniques. But my answers are wrong. If I could at least a hint how to start the problems, that will be great. Thank you http://in.answers.yahoo.com/question/index?qid=20070913001344AAUQAZ2
From: John C. Polasek on 30 Sep 2007 20:23 On Sun, 30 Sep 2007 04:57:39 -0000, shreemayeede(a)gmail.com wrote: >I need hep with these three problems: > >1) A block is hung by a string from the inside roof of a van. When >the van goes straight ahead at a speed of 23 m/s, the block hangs >vertically down. But when the van maintains this same speed around an >unbanked curve (radius = 150 m), the block swings toward the outside >of the curve. Then the string makes an angle theta with the vertical. >Find theta. > >2) Your baggage is on a carousel at an airport. Your suitcase has not >slid all the way down the slope and is going around at a constant >speed on a circle (r = 12.6 m) as the carousel turns. The coefficient >of static friction between the suitcase and the carousel is 0.760, and >the angle that the baggage on the carousel makes with the horizontal >plane is 36.0�. How much time is required for your suitcase to go >around once? > >3) In an automatic clothes drier, a hollow cylinder moves the clothes >on a vertical circle (radius r = 0.39 m). The appliance is designed so >that the clothes tumble gently as they dry. This means that when a >piece of clothing reaches an angle of above the horizontal, it loses >contact with the wall of the cylinder and falls onto the clothes >below. How many revolutions per second should the cylinder make in >order that the clothes lose contact with the wall when theta = 72.0�? > >Thank you very much for your help. Ok for #1, the horizontal acceleration is V^2/R. The vertical acceleration is 9.8m/ss. tan phi = horizontal/vertical. John Polasek
From: Puppet_Sock on 1 Oct 2007 11:33 On Sep 30, 3:16 pm, shreemaye...(a)gmail.com wrote: [snip do-my-homework whine] > The post that told me to read my book or to pay attention in lecture, > I have done so. I have drawn vector diagrams, I have tried a lot of > different techniques. But my answers are wrong. If I could at least a > hint how to start the problems, that will be great. Hint 1) Show what you have done to try to do your own homework. Hint 2) Repeat after me: "Do you want fries with that?" Socks
From: Eric Gisse on 1 Oct 2007 18:27 On Sun, 30 Sep 2007 19:16:09 -0000, shreemayeede(a)gmail.com wrote: [...] >The post that told me to read my book or to pay attention in lecture, >I have done so. I have drawn vector diagrams, I have tried a lot of >different techniques. But my answers are wrong. If I could at least a >hint how to start the problems, that will be great. > >Thank you If you can't solve *any* of these problems yourself, I highly suggest changing majors.
From: xray4abc on 2 Oct 2007 21:15
On Sep 30, 12:57 am, shreemaye...(a)gmail.com wrote: > I need hep with these three problems: > > 1) A block is hung by a string from the inside roof of a van. When > the van goes straight ahead at a speed of 23 m/s, the block hangs > vertically down. But when the van maintains this same speed around an > unbanked curve (radius = 150 m), the block swings toward the outside > of the curve. Then the string makes an angle theta with the vertical. > Find theta. > > 2) Your baggage is on a carousel at an airport. Your suitcase has not > slid all the way down the slope and is going around at a constant > speed on a circle (r = 12.6 m) as the carousel turns. The coefficient > of static friction between the suitcase and the carousel is 0.760, and > the angle that the baggage on the carousel makes with the horizontal > plane is 36.0°. How much time is required for your suitcase to go > around once? > > 3) In an automatic clothes drier, a hollow cylinder moves the clothes > on a vertical circle (radius r = 0.39 m). The appliance is designed so > that the clothes tumble gently as they dry. This means that when a > piece of clothing reaches an angle of above the horizontal, it loses > contact with the wall of the cylinder and falls onto the clothes > below. How many revolutions per second should the cylinder make in > order that the clothes lose contact with the wall when theta = 72.0°? > > Thank you very much for your help. First thing to do is, to choose a reference frame to analyze the situation. Stick to it to the very end ! All forces you consider must be from the frame you have chosen. (Do not mix them ! This is the main mistake, done by students, which stops them from solving the problem!) Draw the diagram of forces. Write the vectorial equilibrium equation. Split it to 2 scalar equations (typically) using a Cartesian coordinates system. Solve the equation system, which results for the components, for the required quantities. Regards, LL |