# Physics

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Any help pleeeze!! I'm totally lost on these!!

1. A 14 g coin slides upward on a surface that is inclined at an angle of 16° above the horizontal. The coefficient of kinetic friction between the coin and the surface is 0.23; the coefficient of static friction is 0.31. Find the magnitude and direction of the force of friction under the following circumstances.
(a) when the coin is sliding
.03 N

parallel to the incline
up the incline
down the incline

(b) after it comes to rest
.012 N

parallel to the incline
down the incline
up the incline

2. A 80 kg astronaut and a 1300 kg satellite are at rest relative to the space shuttle. The astronaut pushes on the satellite, giving it a speed of 0.23 m/s directly away from the shuttle. Seven-and-a-half seconds later the astronaut comes into contact with the shuttle. What was the initial distance from the shuttle to the astronaut?
1.725 m

3. Find the orbital speed of a satellite in a circular orbit 2540 km above the surface of the Earth.
215320 km/s

4. The force shown in Figure 7-16 acts on a 1.7 kg object whose initial speed is 0.44 m/s and initial position is x = 0.27 m.

Figure 7-16
(a) Find the speed of the object when it is at the location x = 0.85 m.
.74 m/s
(b) At what location would the object's speed be 0.40 m/s?
.46 m

one question per post please.

On the first, how is static friction less than sliding friction?

On the second, I don't get that answer. I will be happy to critique your work.

I didn't look at three or four (no figure).

I'm having problems with a friction question. here it is..

1. A 14 g coin slides upward on a surface that is inclined at an angle of 16° above the horizontal. The coefficient of kinetic friction between the coin and the surface is 0.23; the coefficient of static friction is 0.31. Find the magnitude and direction of the force of friction under the following circumstances.

(b) after it comes to rest up the incline

.012 N

I've been using my book and trying to get this for about an hour and I'm at a complete loss.

I will be happy to critique your work.

ok well i thought it would be the same as finding the kinetic friction.. since now we're looking for static friction.

first i looked for the normal force. since mg = the coins weight and because we're on an incline i used mgSin(theta) to find the perpendicular force which is the normal force in this case. Then i multiplied it times the coefficient of static friction and i got .012. but evidently that's not right. Except my book doesnt give you a clear description of how to do static friction. kinetic friction yes, but not static.

all correct, except for mgSinTheta. You should be using CosineTheta.

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