Engineering Mechanics – Statics - tutorial 1

Dr. Ing. Zdenka Sant

Engineering Mechanics – Statics

Tutorial sheet

V. Friction

29. The uniform pole has a weight of 150 N and a

length of 7.8 m. If it is placed against the smooth

wall and on the rough floor in the position d = 3 m,

will it remain in this position when it is released?

The coefficient of static friction is

s = 0.3.

30. The block brake is used to stop

the wheel from rotating when the

wheel is subjected to a couple

moment Mo. If the coefficient of

static friction between the wheel

and the block is s, determine the

smallest force P that should be

applied.

31. Two blocks A and B have a weight of 10 N and 6 N, respectively. They are

resting on the incline for which the coefficients of static friction are A =

0.15 and B = 0.25. Determine the incline angle for which both blocks

begin to slide. Also find the

required stretch or compression

in the connecting spring for

this to occur. The spring has a

stiffness of k = 2 Nm-1

.

32. The linkage shown connects two

blocks A and B, each having a mass

of 6 kg. If the coefficients of static

friction at the contacting surfaces are

A = 0.2 and B = 0.8, determine the

largest vertical force P that may be

applied to pin C without causing the

blocks to slip. Neglect the weight of

the links.

Engineering Mechanics – Statics - tutorial 2

Dr. Ing. Zdenka Sant

33. The coefficient of static friction between wedges

B and C is s = 0.6 and between the surfaces of

contact B and A and D, s’ = 0.4. If the spring is

compressed 200 mm when in the position shown,

determine the smallest force P needed to move

wedge C to the left. Neglect the weight of the

wedges.

34. The square-threaded screw has a mean

diameter of 20 mm and lead of 4 mm. If the

weight of the plate A is 50 N, determine the

smallest coefficient of static friction between

the screw and the plate so that the plate does

not travel down the screw when the plate is

suspended as shown.

35. Determine the

maximum and the minimum values of weight

W, which may be applied without causing the

50 N blocks to slip. The coefficient of static

friction between the block and the plane is s

= 0.2, and between the rope and the drum D

s’ = 0.3.

36. The conveyer belt is used to transfer granular material and the frictional

resistance on the top of the belt is F = 500 N. Determine the smallest stretch

of the spring attached to the moveable axle of the idle pulley B so that the

belt does not slip at the drive pulley A when the torque M is applied. What

minimum torque M is required to keep the belt moving? The coefficient of

static friction between

the belt and the wheel at

A is s = 0.2.

37. The annular ring bearing is subjected to a thrust of 4000 N. If s = 0.35,

determine the torque M that must be applied to overcome friction.

Engineering Mechanics – Statics - tutorial 3

Dr. Ing. Zdenka Sant

38. The pivot bearing is subjected to a

pressure distribution at its surface of

contact, which varies as shown. If the

coefficient of static friction is s,

determine the torque M required to

overcome friction if the shaft supports

an axial force P.

39. Determine the tension T in the belt

needed to overcome the tension of

200 N created on the other side.

Also, what are the normal and

frictional components of force

developed on the collar bushing?

The coefficient of static friction is s

= 0.21.

40. The lawn roller weighs 1500 N. If the rod BA is held at an angle of 300 from

the horizontal and the coefficient of rolling resistance for the roller is 50

mm, determine the force F needed to push the roller at constant speed.

Neglect friction developed at the axle and assume that the resultant force

acting on the handle is applied along BA.