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Physics Probems

post #1 of 7
Thread Starter 
Gifts to anyone who can help:

1)A 2.00 kg block is pushed against a spring with negligible mass and force constant k = 400 N/m, compressing it 0.220 m. When the block is released, it moves along a frictionless, horizontal surface and then up a frictionless incline with slope 37.0 degrees .

a)What is the speed of the block as it slides along the horizontal surface after having left the spring?

b)How far does the block travel up the incline before starting to slide back down?

2) Suppose that the coefficient of friction between your feet and the floor, while wearing socks, is 0.250. Knowing this, you decide to get a running start and then slide across the floor.

a) If your speed is 3.00 m/s when you start to slide, what distance d will you slide before stopping?

F*d = 1/2mv^2
.250m(9.8 )*d = 1/2m(3)^2
d = 1/2(3)^2 / .25(9.8 )
d = 1.8367 m

b) Now, suppose that your young cousin sees you sliding and takes off her shoes so that she can slide as well (assume her socks have the same coefficient of friction as yours). Instead of getting a running start, she asks you to give her a push. So, you push her with a force of 125 N over a distance of 1.00 m. If her mass is 20.0 kg, what distance d does she slide (i.e., how far does she move after the push ends)? Remember that the friction force is acting anytime that she is moving.

3)A child's toy consists of a block that attaches to a table with a suction cup, a spring connected to that block, a ball, and a launching ramp. (Intro 1 figure) The spring has a spring constant k, the ball has a mass m, and the ramp rises a height y above the table, the surface of which is a height H above the floor.

Initially, the spring rests at its equilibrium length. The spring then is compressed a distance s, where the ball is held at rest. The ball is then released, launching it up the ramp. When the ball leaves the launching ramp its velocity vector makes an angle theta with respect to the horizontal.

Throughout this problem, ignore friction and air resistance.

a) Calculate v_r, the speed of the ball when it leaves the launching ramp.
Express the speed of the ball in terms of k, s, m, g, y, and/or H.

b) With what speed will the ball hit the floor?
Express the speed in terms of k, s, m, g, y, and/or H.

4) A bungee cord is 30.0 m long and, when stretched a distance x, it exerts a restoring force of magnitude kx. Your father-in-law (mass 91.0 kg) stands on a platform 45.0 m above the ground, and one end of the cord is tied securely to his ankle and the other end to the platform. You have promised him that when he steps off the platform he will fall a maximum distance of only 41.0 m before the cord stops him. You had several bungee cords to select from, and you tested them by stretching them out, tying one end to a tree, and pulling on the other end with a force of 390 N.

a)When you do this, what distance will the bungee cord that you should select have stretched?

5) A 62.0-kg skier starts from rest at the top of a ski slope of height 66.0 m.

a) If frictional forces do −1.08×104 J of work on her as she descends, how fast is she going at the bottom of the slope?
Take free fall acceleration to be g = 9.80 m/s^2.

b) Now moving horizontally, the skier crosses a patch of soft snow, where the coefficient of friction is 0.22. If the patch is of width 69.0 m and the average force of air resistance on the skier is 150 N, how fast is she going after crossing the patch?

c)After crossing the patch of soft snow, the skier hits a snowdrift and penetrates a distance 2.6 m into it before coming to a stop. What is the average force exerted on her by the snowdrift as it stops her?
post #2 of 7
I'm assuming this chapter is probably just some sort of kinematics focusing on Hooke's law and Work. I think, you should (if your professor hasn't mentioned this!) start by drawing a diagram of each situation. Always, always draw a picture. Choose which directions will be positive and negative axes. Write down what you're given, and what you're solving for. You probably have a plethora of equations in this and preceding sections of the book. It's mostly just plugging stuff in with the correct units.

The only way to learn how to solve problems is to solve problems. This includes struggling with them. When you solve problems like these, it doesn't matter whether or not you get the correct answer- what matters is the problem-solving process. If you're taking half an hour to an hour to solve each problem... then I'd say that's pretty normal and nothing to be worried about.

Look in your book for examples. If you're really struggling with the material, maybe you can make some study buddies in the class and/or look for a tutor. If you can find where the Physics nerds hang out (like the Society of Physics Students clubroom, if there's one on your campus), I would just wander in and ask if anybody is willing to help you. Physics majors are raging know-it-alls (or is it knows-it-all?). I think someone will volunteer their time.

But seriously, asking for help on that many problems over the internet does not seem beneficial to you.
post #3 of 7
Sorry I can't be of any help...I am now worried that my socks have a different coefficient of friction than my hubby's
post #4 of 7
You know, I honestly don't know why I open these threads, although when I started reading it, I thought maybe it was a creative way of describing a disaster at your house! Alas, I was disappointed. Sorry I couldn't be any help but I now have a headache and feel very stupid .
post #5 of 7
Unfortunately I am as stumped as you are right now!!! I am working on centripetal force and kinetic friction and work for oh.....9 hours today??? Can't seem to get anything!!!! Physics has absolutely beaten me up!!! GOOD LUCK TO YOU!!!!!!!!!!
post #6 of 7
All these questions seem like basic kinematics, so pull up a bunch of physics books and start going through problems. I'm sure you can find this stuff on the net, too. You'll figure out formulas and methods of solving it eventually.

All I recall from springs are F=-kx and I think you can say F=mg sin theta or something or other. It's been a while since I took Physics I!

Sorry this doesn't help, but physics is all about doing several problems and then understanding the mechanism i.e. application of formulae behind solving them.
post #7 of 7
The problems you're describing sound exactly like my AS/A-level mechanics lessons, which I passed by the skin of my teeth, and hated every minute.

Just reading the questions has given me a headache
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