Deck 9: Friction

Question 1

A train is travelling at 90 km/h and has wheels of diameter 1600 mm. (a) Find the angular velocity of the wheels in both rad/s and rev/min. (b) If the speed remains constant for 2 km, determine the number of revolutions made by a wheel, assuming no slipping occurs.

Answer 1

Question 2

The speed of a shaft increases uniformly from 200 revolutions per minute to 700 revolutions per minute in 12 s. Find the angular acceleration, correct to 3 significant figures.

Answer 2

Question 3

Answer 3

Question 4

The material of a brake is being tested and it is found that the dynamic coefficient of
friction between the material and steel is 0.90. Calculate the normal force when the frictional force
is 0.630 kN.

Question 5

Question 6

Question 7

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 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.

Question 8

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.

Question 9

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 fulcrum and effort is 1.6 m. Assume the lever is 100% efficient.