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This set of Machine Kinematics Multiple Choice Questions & Answers (MCQs) focuses on “Friction of a V-thread”.

1. Which of the following screw thread is used for jacks, vices and clamps?

Explanation: The square threads are employed in screw jacks, presses and clamping devices.

2. Which of the following screw thread is used for transmitting force in one direction?

Explanation: A buttress thread, is used when large forces act along the screw axis in one direction only. This thread combines the higher efficiency of square thread and the ease of cutting and the adaptability to a split nut of acme thread.

3. Which of the following screw thread is adaptable to split type nut?

Explanation: An acme or trapezoidal thread, is a modification of square thread. The slight slope given to its sides lowers the efficiency slightly than square thread and it also introduce some bursting pressure on the nut, but increases its area in shear. It is used where a split nut is required and where provision is made to take up wear as in the lead screw of a lathe.
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4. Which of the following screw thread is stronger than other threads?

Explanation: Buttress thread is stronger than other threads because of greater thickness at the base of the thread. The buttress thread has limited use for power transmission. It is employed as the thread for light jack screws and vices.

5. Which of the following screw thread is used for lead screw of lathe?

Explanation: The square threads are employed in screw jacks, presses and clamping devices.

6. For self locking screw
a) φ > α
b) α > φ
c) μ < tanα
d) μ = cosecα

Explanation: If φ < α, then torque required to lower the load will be negative. In other words, the load will start moving downward without the application of any torque. Such a condition is known as over hauling of screws. If however, φ > α, the torque required to lower the load will be positive, indicating that an effort is applied to lower the load. Such a screw is known as self locking screw.

7. For over hauling screw
a) φ > α
b) α > φ
c) φ > α
d) none of the mentioned

Explanation: If φ > α, then torque required to lower the load will be negative. In other words, the load will start moving downward without the application of any torque. Such a condition is known as over hauling of screws. If however, φ > α, the torque required to lower the load will be positive, indicating that an effort is applied to lower the load. Such a screw is known as self locking screw.

8. A cup is provided in screw jack
a) to reduce the friction
b) to prevent rotation of load
d) to increase efficiency

Explanation: For the prevention of the rotation of load being lift, the load cup of a screw jack is made separate from the head of the spindle.

9. The maximum efficiency of square threaded power depends upon
b) friction angle
c) pitch of screw
d) nominal diameter of screw

Explanation: The efficiency of a square threaded screw depends upon the helix angle α and the friction angle φ.

10. The efficiency of square threaded power depends upon
a) mean diameter of screw
b) coefficient of friction
c) pitch of screw
d) all of the mentioned