Can someone help me work this physics problem?

Question

Please don't respond for the sake of points. When people who don't know anything about the question answer, other people will think the question is resolved.

The drawing shows a large cube (mass = 38 kg) being accelerated across a horizontal frictionless surface by a horizontal force P. A small cube (mass = 2.7 kg) is in contact with the front surface of the large cube and will slide downward unless P is sufficiently large. The coefficient of static friction between the cubes is 0.71. What is the smallest magnitude that P can have in order to keep the small cube from sliding downward?

Here is the picture http://i21.photobucket.com/albums/b272/Cajunboiler/Physics_.gif

How do I work this? What is the answer?

Mr. Midget, that answer is wrong according to the homework.

Odu83, what numbers would I plug in though?

According to the website, 13.8 is wrong.

The way the website works is that I have a certain number of answers I can submit (5) and it tells me if it's wrong or right (I've used 3 submissions already on that problem)

561.7 is correct. Thank you for the help.

Daria, I am doing the majority of my homework by myself. Certain problems I have questions with and don't know how to work them. I come to yahoo answers to get help, not to be criticized.

Answer 1

I'll help

This is a simple problem turned on it's side.

The force acting on the 2.7 kg block is gravity in the verticle and P in the horizontal.

Fmax = us N

The force on the block in the vertical is 2.7 * 9.8 = 26.46

The horizontal force is P * 2.7 which is N

so Pmin = 26.46/(.71*2.7)
=13.8

j

Answer 2

Suppose that w is the weight of the small cube, F is the friction force and N the force acted on the small cube by the large (draw them). Now

w = m*g = 2.7*9.81 = 26.5 N, where m the mass of the small cube and g the acceleration of gravity.

In order not to slide, we have:

F = w, F = 26.5 N

But F = h*N => N = F/h = 26.5/0.71= 37.3 N, where h the coefficient of friction.

We can find now the acceleration a with which both cubes are moved:

N = m*a => a = N/m = 37.3/2.7 = 13.8 m/s^2

According to the Newton's second law:

P = (M + m)*a = (38 + 2.7)*13.8 = 561.7 N, where M the mass of the large cube.

So P >= 561.7 N

Answer 3

The small cube will slide downward anyway even if you apply a large force. Secondly the smallest magnitude of P will be very very less since the surface is frictionless and the body will continue in its state of motion.

Answer 4

I'm a little rusty on this but i think i got it.

just you know what I'm doing:
F is friction force between the small and large cubes
P is already defined
U is coefficient of friction=.71
W is weight of the small cube

the way I'd do this is draw a force diagram of the small cube

pointing up is F, down is W (2.7*9.8=26.46) and pointing right is P

F=W, it's in equilibrium so net force is zero

so you should know that F=U*P (variation of: friction force= mue times normal force)

so you know F and U so pug it in:

26.46=.71*P

(26.46)/(.71)=P

37.26=P and units would be newtons


if you know the answer tell me then i'll work backwards for you

Answer 5

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Answer 6

well, i looked at your problem, but my class hasn't covered that yet. you could try looking on a home work help site, or call a phone number. i'm sorry i couldn't help.

Answer 7

Sorry i just wanted to wish you luck. And also, you should do things yourself.