Help please with physicsss

help please guys with this

http://img256.imageshack.us/img256/2972/img0969uo.jpg

regards

Take torques about the base of the ladder to eliminate the unknown force R and get an expression for P in terms of F and W. The net torque must be 0 for no angular acceleration.

τ = 0 = P*20*sin 58 - F*12*sin 32 - W*7.5*sin 32
20P * sin 58 = (12F + 7.5W) sin 32
20P * cos 32 = (12F + 7.5W) sin 32
P = (tan 32)(12F + 7.5W)/20

Plug in F and W to get then answer to part (a).

For (b), split R into Rx horizontally and Ry vertically, and set the horizontal and vertical sums of forces to 0, independently. (Both must be 0 for no linear acceleration.)

0 = Ry - F - W
0 = Rx - P

So the component of R are (P, F+W), the magnitude is sqrt(P² + (F+W)²) and the direction is given by tan φ = (F + W)/P, φ = arctan[ (F + W)/P ]

Look at the diagram: F=weight of man, W=weight of ladder

Report Abuse

Take moments about the base of the ladder noting that P is perpendicular to the wall because the wall is 'smooth'.
Next, sum the vertical and horizontal forces to determine the vertical and horizontal components of R.
Once you have these components use Pythagoras formula for the magnitude of the resultant.
Use theta = arctan(vert. component/horz. component) for the direction of R.