# Search results

1. ### Differential equations help!

Homework Statement this problem was on my finals and i stared at it for 30 mins straight and still didn't figure it out and now it just bothers me that i don't know how to do the first problem on my final exam. "find the general solution to the dfq" xy'+xy= 1-y Homework Equations...
2. ### Nonhomogeneous diff equations method of undeterined coeff.

Homework Statement Find the general solution to the diff equation using undetermined coefficients y''-2y'-3y = 3te^-1 Homework Equations The Attempt at a Solution r^2 - 2r -3 = 0 r = -1, 3 so y = c1 e^-t + c2e^3t + yp since e^-t already exists as a solution, i have to...
3. ### Differential Equations reduction of order

Homework Statement Find y2 given t^2y'' + 3ty' + y = 0 y1(t) = 1/t Homework Equations The Attempt at a Solution i found y, y' and y'' and plugged it back in to the Differential equation, after doing some work, i'm basicly down to tv''+v' = 0 where y2 = v/t so u =...
4. ### Integrating factor confusion

Homework Statement Solving this differential equation ty' + 2y = t^2 - t + 1 Homework Equations Its linear so i set it up in linear form y' + y(2/t) = t - 1 +1/t The Attempt at a Solution the integrating factor (u) = e ^ integral (ydt) = e^ integral (2dt/t)... Here's the...
5. ### Floating bed problem

Homework Statement There is a large bed floating in sea with the density of 765 kg/m^3. What fraction of the bed's volume will be under the surface of the water? The density of sea water is 1035 kg/m^3. Homework Equations Fb = Density * v * gravity The Attempt at a Solution I know...
6. ### Block on a roller coaster

Homework Statement A small cube (m=0.450 kg) is at a height of 393 cm up a frictionless track which has a loop of radius, R = 58.95 cm at the bottom. The cube starts from rest and slides freely down the ramp and around the loop. Find the speed of the block when it is at the top of the loop...
7. ### Weight in water

Homework Statement An object weighing 341 N in air is immersed in water after being tied to a string connected to a force scale. The scale now reads 307 N. Calculate the density of the object. Homework Equations Fb=(density of the surrounding liquid)(V)(g) The Attempt at a...
8. ### Diameter of a wire

Homework Statement Find the minimum diameter of an l = 17.2 m long steel wire that will stretch no more than 7.38 mm when a mass of 323 kg is hung on the lower end. (Hint: The Young's modulus of steel is 200.0 GPa.) Homework Equations Youngs = (Force / Area) / (change L / L)...
9. ### Damped Oscillator and time

Homework Statement A mass M is suspended from a spring and oscillates with a period of 0.880 s. Each complete oscillation results in an amplitude reduction of a factor of 0.96 due to a small velocity dependent frictional effect. Calculate the time it takes for the total energy of the...
10. ### Potential Grav. Energy to Kine. Energy Problem

Homework Statement On a roller coaster ride the total mass of the cart - with passengers included - is 280 kg. Peak K is at 46.0 m above the ground, peak L is at 21.5 m. The speed of the cart at K is 17.1 m/s, at L it is 12.8 m/s. How much energy is lost due to friction between the two peaks...
11. ### Sliding down a Track, loop, Conservation problem

Homework Statement A small cube (m=0.450 kg) is at a height of 393 cm up a frictionless track which has a loop of radius, R = 58.95 cm at the bottom. The cube starts from rest and slides freely down the ramp and around the loop. Find the speed of the block when it is at the top of the loop...
12. ### Sphere rolling down a ramp problem

Homework Statement A solid sphere of uniform density (weight = 3.2 lbs starts from rest and rolls down a ramp (H = 1.57 m, q = 18.3°.) Find the speed of the sphere's CM when it reaches the bottom of the ramp. haha sorry bout that.... Homework Equations see below The Attempt at...
13. ### Four mass and Tension problem

Homework Statement Four blocks are on a horizontal surface. The blocks are connected by thin strings with tensions Tx, Ty, Tz. The masses of the blocks are A=22.0 kg, B=21.0 kg, C=17.0 kg, D=27.0 kg. Two forces, F1=83.0N and F2=50.0N act on the masses as shown. Assume that the friction...
14. ### Kinetic Friction Coefficient Problem

Homework Statement A block is at rest on a plank whose angle can be varied. The angle is gradually increased from 0 deg. At 26.5°, the block starts to slide down the incline, traveling 3.10 m down the incline in 2.00 s. Calculate the kinetic coefficent of friction between the block and the...
15. ### Lifting a mass problem

Homework Statement A 1.65 kg mass is suspended from a string which is pulled upward. The mass accelerates upwards with an acceleration of 3.10 m/s^2. What is the tension in the string? Homework Equations f = ma The Attempt at a Solution seems really easy but i can't get the right answer...
16. ### Newton's law trick? question

Newton's law "trick?" question Homework Statement A 40 kg girl and a 50 kg boy are on the surface of a frozen lake, 10 m apart. Using a rope, the girl exerts a horizontal 5.0 N force on the boy, pulling him toward her. Calculate the magnitude of the girl's acceleration. Homework Equations...
17. ### Trajectory, does it clear a certain height problem help!

Trajectory, "does it clear a certain height" problem help! Homework Statement A place kicker must kick a football from a point 45.5 m from the goal, and the ball must clear the crossbar, which is 3.05 m high. When kicked, the ball leaves the ground with a speed of 19.0 m/s at an angle of 48.0°...
18. ### Faraday's law problem

Homework Statement Take a loop of wire with a radius of 2.0 cm. A B field is perpendicular to the area enclosed by the wire. If the field is reduced to zero from 0.55 T in 0.25 s, what is the induced emf between the ends of the wire? Homework Equations B=Magnetic Field A=Area Flux=...
19. ### Colums law problem

Homework Statement Take three charged objects and place them on the x-axis. The first charge is + 11 microC, and is placed at +0.85 m. The second charge is -4.6 microC, and is placed at -0.22 m. The third charge is placed at the origin. If the net force on the third charge has a magnitude of...
20. ### Basic Wave question

Homework Statement Shake a rope so that it makes three "humps" (known more formally as anti-nodes). If you shake the rope up & down 12 times in 9.5 seconds while you and your partner are 2.5 m apart, what is the speed of the wave through the rope? Homework Equations...
21. ### Pressure of water problem

Homework Statement The density of fresh water is 1000 kg/m3. Normal air pressure (i.e., 1 atm) is 1.013(105) Pa. If someone were beneath 25.0 m of water, what pressure would they experience? Give your answer in Pascals and in atmospheres. Homework Equations i guess the (density of...
22. ### Solids, Young's Modulus

Homework Statement Hang a 0.25 kg rock from the end of a spring. If the spring stretches 0.25 m, what is the spring constant? Homework Equations i'd assume F/A=Y(Change in L/Lo) The Attempt at a Solution I can do it if there was Area, but there isn't. there's probably another...
23. ### Help on Moment of inertia again thanks =D

Homework Statement I need one more question answered =D thanks A man is standing on a spinning turntable with a weight in each hand. His moment of inertia with arms outstretched is 16Nm. WIth his arms by his sdie his moment of Inertia is 6.4Nm. With arms outstreched he makes one rotation in...
24. ### Centripetal force/acc problem

Homework Statement What angular velocity would cause a centripetal acceleration of 3 g's if the radius were 2.5 m? i have a test 2moro on this stuff... yea i need to know =D thx Homework Equations i guess m(v^2)/r or mW^2r The Attempt at a Solution no idea. srry :confused:
25. ### Need help/varify on a torque/moment of inertia problem

Homework Statement Hi, this is my first time on this forum, so don't flame me for not doing things right. I'm a junior in high school and currently taking AP physics, this problem in my hwk has been bothering me for a while. I've never recieved the answer to this question and i jsut need to...
26. ### Need verify on a momment of inertia/torque problem

Hi, this is my first time on this forum, so don't flame me for not doing things right. I'm a junior in high school and currently taking AP physics, this problem in my hwk has been bothering me for a while. I've never recieved the answer to this question and i jsut need to know if i did this...