Physics Problems - not impossible

Discus: SAT/ACT Tests and Test Preparation: October 2003 Archive: Physics Problems - not impossible
 By Jason817 (Jason817) on Saturday, October 04, 2003 - 09:54 pm: Edit

1. A block of mass 2 kg slides along a horizontal tabletop. A horizontal applied force of 13 N and a vertical applied force of 15 N (downward) act on the block. If the coefficient of friction between the block and the table is 0.2, find the approximate frictional force on the block.

2. A traffic light of weight 100 N is supported by two ropes each tied to a horizontal pole. Each rope is making a 37 degree angle with the pole (essentially making an isoceles triangle). What is the tension of each rope?

3 (easy one). If you exert a force F on an object, the magnitude of the force that the object exerts on you _______.

Is it:
a) will depend on whether or not the object is moving
b) will depend on whether or not you are moving
c) will depend on the relative masses of you and the object
d) will be F in all cases
e) none of the above

 By Jason817 (Jason817) on Saturday, October 04, 2003 - 11:37 pm: Edit

bump

 By Ti89 (Ti89) on Sunday, October 05, 2003 - 01:33 am: Edit

I don't know if this is right, but I'll give it a shot:

1. F[A] = 13_N (do you do anything with this?)
15_N down
F[G]=mg, F[G]=(2_kg)(9.8_m/_s^2)=19.6_N (force of gravity)
Fdown = 15 N + F[G] = 34.6_N
Ffr = mu[k]*F[N] = (0.2)(34.6_N) = about 7 N

3. d. Newton's law

 By Heartfang2 (Heartfang2) on Sunday, October 05, 2003 - 02:12 am: Edit

1. Resolve the force vertically

(taking the gravitational force as 10m/s^2)

R(Reaction)= 15 + 2(10)
= 35 N

Resolve the force horizontally

Friction = 0.2 x R
= 0.2 x 35
= 7 N

_____________________________________________
2. Since the two tensions are the same

Let T=Tension
2T cos 37 = 100
Solve for T..

 By Yz16 (Yz16) on Sunday, October 05, 2003 - 02:27 am: Edit

i agree with Ti89...
for number 2) i think this is resolving forces etc.
We're going to start this stuff in class soon actually, but for now i got this eqn:
if x is the tension,
100N = 2(xcos53)
x is then um ... 83N?

not sure. : )

 By Jason817 (Jason817) on Sunday, October 05, 2003 - 03:24 am: Edit

thanks.

#2 was actually multiple choice. Both your answers are one of the choices.

A. 83 N
B. 66 N
C. 63 N
D. 50 N
E. None of the above

 By Jason817 (Jason817) on Sunday, October 05, 2003 - 03:27 am: Edit

oh and I'd appreciate it if you can help me with this one. I posted it before but no one could do it. The pic is in my profile.

A large box (m=25.0 kg) is pushed to the right with an applied force of F across a frictionless table. A second, small box (m=4.00 kg) is in contact with the front of the box. If the coefficient of friction between the two boxes is 0.710, calculate the minimum value of F so that the small box does not slide down the face of the larger box. Hint: The reaction force between the 4.00 kg and 25.0 kg boxes is the normal force for the 4.0 kg box

 By Sidis (Sidis) on Sunday, October 05, 2003 - 11:03 am: Edit

Why don't you ask your physics' teacher? THis is a SAT area not a Homeworkcraking place...

don't take it personal

 By Jason817 (Jason817) on Sunday, October 05, 2003 - 11:44 am: Edit

well first of all, i cant contact him during the weekends, and secondly, we have a quiz on the chapter coming up so if I do these practice problems (not my homework btw) during the weekend, I would be better prepared.

 By Desibrij_1785 (Desibrij_1785) on Sunday, October 05, 2003 - 12:29 pm: Edit

Proton Bombardment. A proton with mass is propelled at an initial speed of directly toward a uranium nucleus 5.00 m away. The proton is repelled by the uranium nucleus with a force of magnitude , where is the separation between the two objects and . Assume that the uranium nucleus remains at rest. this is the problem and questions are
What is the speed of the proton when it is from the uranium nucleus?

 By Jason817 (Jason817) on Sunday, October 05, 2003 - 01:51 pm: Edit

bump

 By Jszab (Jszab) on Sunday, October 05, 2003 - 02:06 pm: Edit

each rope: mg / 2 sin alfa.
Do You want to have mathematical explain?
Try to resolve this:
[Made my own. I really like it.]
Explain why rope is making angle when it is hanging between two points, and count an angle between ground and rope.
You have K of rope, mass, which is in the center of rope, and lenght of rope, g.
First part is easy, second need some higher trigonometry, or computer. [there will be two trig. functions, and you must find dependancy between them.] hints: jszab@o2.pl

 By Jason817 (Jason817) on Sunday, October 05, 2003 - 05:23 pm: Edit

help?

 By Muawan (Muawan) on Sunday, October 05, 2003 - 06:25 pm: Edit

Proton Bombardment. A proton with mass is propelled at an initial speed of directly toward a uranium nucleus 5.00 m away. The proton is repelled by the uranium nucleus with a force of magnitude , where is the separation between the two objects and . Assume that the uranium nucleus remains at rest. this is the problem and questions are
What is the speed of the proton when it is from the uranium nucleus?

Cannot be answered under classical assumptions.

 By Perry2006 (Perry2006) on Monday, October 06, 2003 - 12:09 am: Edit

Jason, I think I get the answer to ur second physics problem with the help from someone who's really good in physics.

1. Lenthy explanation:
Us * Fn = Fs, Max
Fs, Max = 0.710 * 4 (9.81)

Fs, Max / m = a
so, a = 0.710 * 4 (9.81) / 4 = 0.710 (9.81) = 6.9651 m/s^2

Force for the large block is the Acceleration (which got from above) * (mass of the large block + mass of the small block)
Because BOTH blocks accelerate.

Thus we have:
F = 6.9651 * (25 + 4)
F = 201.988 = 202 N

2. Simplified Reasoning:
M = the mass of the LARGE block
m = the mass of the SMALL block
F = Force, or what we are solving for
N = Normal force
u = friction constant

Since F / (M+m) = a
N * u = mg * u = a * m
We have
g*u = a
a = 6.9651
Thus F = 6.9651 (29)= 202 N

Hope this helps!

 By Joel_Set (Joel_Set) on Monday, October 06, 2003 - 12:33 am: Edit

yo sidis... this is the 2nd sour remark you made for apparently no reason imo.. ppl come to this board to also help one another rather than just solving sat questions.. also this is a TEST PREPARATION area.. he's asking question about ap physics.. which is indeed a TEst(ap).. so shut ur crap if you dunno what the hell you are talking about

 By Jason817 (Jason817) on Monday, October 06, 2003 - 01:09 am: Edit

Perry2006 - Thank you so much. I am incredibly grateful. Thank your friend for me too.

One last hard question (sorry):

The picture is in my profile (yes I have no artistic abilities).

Three masses m1= 2 kg, m2= 5 kg, and m3= 25 kg are connected by a string over a pulley on a rough inclined plane tilted at 25 degrees with the horizontal, as shown. If the masses start at rest and the coefficient of kinetic friction between blocks 1 and 2 and the plane is 0.240, find:

1) the initial acceleration of the system
2) the tension in the connecting string between m1 and m2.

Thanks again.

 By Jason817 (Jason817) on Monday, October 06, 2003 - 06:03 pm: Edit

bump

 By Jason817 (Jason817) on Monday, October 06, 2003 - 09:44 pm: Edit

bump?

 By Jason817 (Jason817) on Wednesday, October 08, 2003 - 06:27 pm: Edit

teh

 By Jason817 (Jason817) on Thursday, October 09, 2003 - 07:35 pm: Edit

I can't seem to do this problem. I was trying for so long. Any help would be appreciated

 By Jason817 (Jason817) on Thursday, October 09, 2003 - 08:02 pm: Edit

can someone at least tell me how to find the horizontal force of m1? That's what I'm stuck on.

 By Jason817 (Jason817) on Thursday, October 09, 2003 - 09:42 pm: Edit

plz! i'm going to kill myself