SIMPLE MACHINES 209
Assignment 5
This assignment covers the material
contained in chapters 15 to 18.
The marks for each question are shown
in brackets at the end of each question.
- The material of a brake is being tested
and it is found that the dynamic coeffi-
cient of friction between the material and
steel is 0.90. Calculate the normal force
when the frictional force is 0.630 kN.
(5)
- A mass of 10 kg rests on a plane, which
is inclined at 30°to the horizontal. The
coefficient of friction between the mass
and the plane is 0.6. Determine the mag-
nitude of a force, applied parallel to and
up the plane, which will just move the
mass up the plane. (10)
- If in Problem 2, the force required to just
move the mass up the plane, is applied
horizontally, what will be the minimum
value of this force? (10)
- A train travels around a curve of radius
400 m. If the horizontal thrust on the
outer rail is to be 1/ 30 ththe weight of the
train, what is the velocity of the train (in
km/h)? It may be assumed that the inner
and outer rails are on the same level and
that the inner rail takes no horizontal
thrust. (6)
- A conical pendulum of length 2.5 m
rotates in a horizontal circle of diameter
0.6 m. Determine its angular velocity,
given that g= 9 .81m/s^2 .(6)
6. Determine the time of oscillation for a
simple pendulum of length 1.5 m. Take
gas9.81m/s^2 .(6)
7. A simple machine raises a load of
120 kg through a distance of 1.2 m. The
effort applied to the machine is 150 N
and moves through a distance of 12 m.
Taking g as 10m/s^2 , determine the force
ratio, movement ratio and efficiency of
the machine. (6)
8. Aloadof30kgisliftedbyathree-
pulley system and the applied effort is
140 N. Calculate, taking g to be 9.8m/s^2 ,
(a) the force ratio, (b) the movement
ratio, (c) the efficiency of the system.
(5)
9. A screw-jack is being used to support
the axle of a lorry, the load on it being
5.6 kN. The screw jack has an effort of
effective radius 318.3 mm and a single-
start square thread, having a lead of
5 mm. Determine the efficiency of the
jack if an effort of 70 N is required to
raise the car axle. (6)
- A driver gear on a shaft of a motor
has 32 teeth and meshes with a follower
having 96 teeth. If the speed of the motor
is 1410 revolutions per minute, find the
speed of rotation of the follower.
(4)
- The load on a first-order lever is 1.5 kN.
Determine the effort, the force ratio and
the movement ratio when the distance
between the fulcrum and the load is
0.4 m and the distance between the ful-
crum and effort is 1.6 m. Assume the
lever is 100% efficient. (6)
