Physics 2 Ch11 Problems

8/12/2019 Physics 2 Ch11 Problems

1/14

Physics 2

Chapter 11 problems

Prepared by Vince Zaccone

For Campus LearningAssistance Services at UCS


2/14

11.44 A pickup truck has a wheelbase of 3m. Ordinarily 10,780N rests on thefront wheels and 8,820N on the rear wheels when parked on a level road.a) A box weighing 3600N is now placed on the tailgate, 1m behind the rear axle.

How much total weight now rests on the front wheels? On the rear wheels?b) How much weight would need to be placed on the tailgate to make the front

wheels come off the ground?

It will be useful to find the center of mass of the truck before the weight is addedto the tailgate. Choosing x=0 at the rear axle:

m65.1107808820

)3)(10780()0)(8820(xcm

We have a couple of options to solve this problem.We could continue to use center of mass ideas, or we could use torques.Both methods give pretty much the same formulas.

Balancing torques (remember, clockwise is negative):

FfrontFrear

3600 N

19,600 N

Pivot Pointx=0 here

N9590F

0)0)(F()m65.1)(N19600()m1)(N3600(

front

front

We could use another torqueequation with the pivot at thefront wheel, or just realize thatthe forces must also balance,leaving a total of 13,610N forthe rear force.

For the final part, we could makethe center of mass come out atthe rear wheel, or force the

torques to balance (with Ffront=0).

N340,32W

0)m65.1)(N19600()m1)(W(




3/14




4/14




5/14


6/14




7/14




8/14

11.72 You are trying to raise a bicycle wheel of massm and radius R up a curb of height h. To do this, youapply a horizontal force F. What is the leastmagnitude of the force F that will succeed in raisingthe wheel onto the curb when the force is applieda) at the center of the wheel?b) at the top of the wheel?c) In which case is less force required?




9/14

11.77 An engineer is designing a conveyor systemfor loading hay bales into a wagon. Each bale is0.25m wide, 0.50m high, and 0.80m long (thedimension perpendicular to the plane of the figure),with mass 30kg. The center of gravity of each haybale is at its geometrical center. The coefficient ofstatic friction between a bale and the conveyor belt is0.60, and the belt moves with constant speed.

a) The angle of the conveyor is slowly increased. Atsome critical angle a bale will tip (if it doesnt slipfirst), and at some different critical angle it will slip(if it doesnt tip first). Find the two critical anglesand determine which happens at the smaller angle.

b) Would the outcome of part (a) be different if thecoefficient of friction were 0.40?




10/14




11/14




12/14

11.87 A 1.05-m long rod of negligible weight is supported at its ends by wiresA and B of equal length. The cross-sectional area of A is 2 mm2and that of Bis 4 mm2. Youngs Modulus for wire A is 1.8x1011Pa; that for B is 1.2x1011Pa.At what point along the rod should weight w be suspended to producea) equal stresses in A and B?b) b) equal strains in A and B?




13/14


14/14


Documents

Physics 2 Ch11 Problems