# Quiz 4 Theory Of Machine Objective questions With Explanation

#### 1. Tooth interference in an external involute spur gear pair can be reduced by

Option ( D) is correct. When gear teeth are produced by a generating process, interference is automatically eliminated because the cutting tool removes the interfering portion of the flank.This effect is called undercutting. By undercutting the undercut tooth can be considerably weakened.So, interference can be reduced by using more teeth on the gear. However, if the gears are to transmit a given amount of power, more teeth can be used only by increasing the pitch diameter.

#### 2. A planar mechanism has 8 links and 10 rotary joints. The number of degrees of freedom of the mechanism, using Gruebler’s criterion, is

Option (B) is correct. From Gruebler’s criterion, the equation for degree of freedom is given by, n = 3(l - 1) - 2j - h ...(i) Given l= 8 and j = 10, h = 0 n = 3(8 - 1) - 2 x 10 = 1

#### 3. For an under damped harmonic oscillator, resonance

Option (C) is correct. For an under damped harmonic oscillator resonance occurs when excitation frequency is equal to the undamped natural frequency wd = wn

#### 4. The number of inversion for a slider crank mechanism is

Option (C) is correct. For a 4 bar slider crank mechanism, there are the number of links or inversions are 4. These different inversions are obtained by fixing different links once at a time for one inversion. Hence, the number of inversions for a slider crank mechanism is 4.

#### 5. The number of degrees of freedom of a planar linkage with 8 links and 9 simple revolute joints is

Option (C) is correct. Given l= 8, j= 9 We know that, Degree of freedom, n = 3(l - 1) - 2j = 3(8 - 1) - 2 x 9 = 3

#### 6. The mechanism used in a shaping machine is

Option (D) is correct. A single slider crank chain is a modification of the basic four bar chain. It is find, that four inversions of a single slider crank chain are possible. From these four inversions, crank and slotted lever quick return motion mechanism is used in shaping machines, slotting machines and in rotary internal combustion engines.

#### 7. The lengths of the links of a 4-bar linkage with revolute pairs are p,q,r, and s units. given that p < q < r < s . Which of these links should be the fixed one, for obtaining a “double crank” mechanism ?

Option (A) is correct. Given p < q < r < s “Double crank” mechanism occurs, when the shortest link is fixed. From the given pairs p is the shortest link. So, link of length p should be fixed.

#### 8. When a cylinder is located in a Vee-block, the number of degrees of freedom which are arrested is

Option (B) is correct. We clearly see from the figure that cylinder can either revolve about x -axis or slide along x -axis & all the motions are restricted. Hence, Number of degrees of freedom = 2 & movability includes the six degrees of freedom of the device as a whole, as the ground link were not fixed. So, 4 degrees of freedom are constrained or arrested.

#### 9. The damping coefficient in the vibration equation is given by

Option is ( C ) correct. From the previous part of the questionDamping coefficient, c = 80 Nms/rad

#### 10. The Coriolis component of acceleration is present in

Option (B) is correct. When a point on one link is sliding along another rotating link, such as in quick return motion mechanism, then the coriolis component of the acceleration must be calculated. Quick return motion mechanism is used in shaping machines, slotting machines and in rotary internal combustion engines.

#### 11. For a spring-loaded roller follower driven with a disc cam,

Option (C) is correct. For a spring loaded roller follower driven with a disc cam, the pressure angle should be large during rise as well as during return for ease of transmitting motion. If pressure angle is large, then side thrust will be minimum. Pressure angles of up to about 30c to 35c are about the largest that can be used without causing difficulties.

#### 12. Which of the following statements is correct ?

Option (A) is correct. The mean speed of the engine is controlled by the governor. If load increases then fluid supply increases by the governor and vice-versa. Flywheel stores the extra energy and delivers it when needed. So, Flywheel reduces speed fluctuations. Flywheel reduce speed fluctuations during a cycle for a constant load, but Flywheel does not control the mean speed ( N= N1+N2 /2 / ) of the engine.

#### 13. At the same instant, if the component of the force at joint A along AB is 30 N, then the magnitude of the joint reaction at O2

Option (D) is correct. From the given data the component of force at joint A along AO2 is necessary to find the joint reaction at O2. So, it is not possible to find the magnitude of the joint reaction at O2.

#### 14 . Match the item in columns I and II

Option (B) is correct.So correct pairs are, P-4, Q-3, R-2, S-1

#### 15. Tooth interference in an external involute spur gear pair can be reduced by

Option ( D) is correct.When gear teeth are produced by a generating process, interference is automatically eliminated because the cutting tool removes the interfering portion of the flank.This effect is called undercutting. By undercutting the undercut tooth can be considerably weakened.So, interference can be reduced by using more teeth on the gear. However, if the gears are to transmit a given amount of power, more teeth can be used only by increasing the pitch diameter.

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