JSSC- JE Mechanical Engg. Question Bank (Chapter – 3)

Mechanical

What is a simple machine?

• A device that changes the magnitude or direction of force
• A device used only for generating electricity
• A device used only for measuring temperature
• A device used only for storing energy

Explanation:

• A simple machine is a mechanical device that helps perform work by changing the magnitude or direction of an applied force.
• Examples include the lever, pulley, wheel and axle, inclined plane, screw, and wedge.
• The ideal mechanical advantage of a machine is the ratio of output force to input force.

What is mechanical advantage of a machine?

• Ratio of output force to input force
• Ratio of input force to output force
• Ratio of output speed to input speed
• Ratio of input work to output work

Explanation:

• Mechanical Advantage (MA) = Load / Effort.
• A machine having MA greater than 1 multiplies the applied force.
• In an ideal machine, input work equals output work.

What is a four-bar linkage?

• A mechanism consisting of four rigid links connected by four turning pairs
• A mechanism having four gears only
• A mechanism having four sliding pairs only
• A mechanism consisting of four independent shafts

Explanation:

• A four-bar linkage consists of four rigid links connected by four pin joints or turning pairs.
• One link is generally fixed and the remaining links produce relative motion.
• It is widely used for converting rotary motion into oscillating or other types of motion.

Which link of a four-bar mechanism is generally fixed?

• Frame or fixed link
• Coupler link
• Rocker link
• Follower link

Explanation:

• The fixed link provides the reference frame for the motion of the other links.
• The other three links are generally called the input link, coupler, and output link.

In a four-bar mechanism, the link connecting the crank and rocker is called the:

• Coupler link
• Frame
• Crank
• Rocker

Explanation:

• The coupler is the floating link that connects the crank and rocker.
• It transmits motion from the input crank to the output rocker.

What is the main function of a flywheel?

• To reduce fluctuation of speed caused by fluctuation of energy
• To control the mean speed of an engine
• To increase friction between gears
• To increase the fuel supply

Explanation:

• A flywheel stores excess energy when the engine produces more energy than required and releases it when the engine produces less energy than required.
• It therefore reduces speed fluctuations within a cycle.
• A flywheel does not normally regulate the mean speed of an engine; that is primarily the function of a governor.

What is fluctuation of energy in an engine?

• The difference between maximum and minimum energy stored in the flywheel during a cycle
• The difference between input and output power at all times
• The total energy supplied by fuel
• The total frictional energy of the engine

Explanation:

• During an engine cycle, the turning moment varies, causing the kinetic energy of the rotating parts to fluctuate.
• Maximum fluctuation of energy is the difference between maximum and minimum values of energy stored in the flywheel during the cycle.
• The flywheel absorbs and releases energy to maintain more uniform speed.

Which device controls the mean speed of an engine when the load changes?

• Governor
• Flywheel
• Clutch
• Brake

Explanation:

• A governor regulates the fuel or working-fluid supply to maintain approximately constant mean speed when the load changes.
• A flywheel mainly reduces cyclic speed fluctuations within an operating cycle.

What is the main purpose of a belt drive?

• To transmit power between two shafts
• To store hydraulic energy
• To measure shaft speed
• To reduce the temperature of a bearing

Explanation:

• A belt drive transmits mechanical power from a driving shaft to a driven shaft using a flexible belt.
• It is suitable when the shafts are separated by a comparatively large distance.

Which type of belt has a trapezoidal cross-section?

• V-belt
• Flat belt
• Round belt
• Rope belt

Explanation:

• A V-belt has a trapezoidal cross-section and operates in a V-grooved pulley.
• The wedging action between the belt and groove increases frictional grip and permits higher power transmission than a flat belt of similar size in many applications.

Which belt is generally preferred for transmitting power over long centre distances?

• Flat belt
• V-belt
• Timing belt only
• Toothed gear belt only

Explanation:

• Flat belts are commonly used for relatively long centre distances.
• V-belts are compact and provide good grip but are generally used for shorter centre distances.
• Flat belts transmit power mainly through friction between the belt and pulley.

What is the main advantage of a V-belt over a flat belt?

• Higher frictional grip due to wedging action
• It requires no pulley
• It cannot slip under any condition
• It always operates without tension

Explanation:

• The V-shaped belt fits into a V-grooved pulley.
• The wedging action increases the normal reaction between the belt and pulley surfaces and consequently increases frictional grip.
• However, V-belts can still slip under unsuitable operating conditions.

What is a clutch?

• A device used to engage or disengage power transmission between two shafts
• A device used only to stop a shaft permanently
• A device used to measure torque
• A device used to store compressed air

Explanation:

• A clutch connects the driving shaft to the driven shaft when power transmission is required.
• It can also disconnect the driven shaft without stopping the prime mover.
• Clutches are widely used in automobiles and machinery.

Which clutch uses friction between flat annular surfaces for power transmission?

• Plate clutch
• Conical clutch
• Centrifugal pump
• Gear clutch

Explanation:

• A plate clutch transmits torque through friction between one or more pairs of flat friction surfaces.
• Single-plate and multi-plate clutches are common types.

In a conical clutch, the friction surfaces are:

• Conical
• Flat circular
• Spherical
• Cylindrical only

Explanation:

• A conical clutch uses mating conical friction surfaces.
• The axial force produces normal pressure on the conical surfaces, allowing torque to be transmitted through friction.

What is the primary function of gears?

• To transmit motion and power between shafts with a definite velocity ratio
• To store electrical energy
• To reduce lubrication requirements to zero
• To eliminate all mechanical losses

Explanation:

• Gears are toothed mechanical elements used to transmit power and motion between rotating shafts.
• They provide a positive drive without the slip associated with friction drives.
• They can also change speed, torque, and direction of rotation.

Which type of gear is used to transmit power between parallel shafts with straight teeth?

• Spur gear
• Bevel gear
• Worm gear
• Rack and pinion

Explanation:

• Spur gears have straight teeth parallel to the axis of rotation.
• They are mainly used for parallel shafts.
• Helical gears are also used for parallel shafts but have inclined teeth.

Which type of gear is generally used to transmit motion between intersecting shafts?

• Bevel gear
• Spur gear
• Worm gear
• Rack and pinion

Explanation:

• Bevel gears have conical pitch surfaces and are commonly used for intersecting shafts.
• They can transmit motion at different shaft angles, commonly 90°.

Which gear arrangement is commonly used for transmitting motion between non-parallel and non-intersecting shafts?

• Worm and worm wheel
• Spur gear pair
• Bevel gear pair
• Rack and pinion

Explanation:

• A worm drive consists of a worm and worm wheel and is commonly used for non-parallel, non-intersecting shafts.
• It can provide a large speed reduction in a compact arrangement.

What is the gear ratio of a pair of gears in terms of their number of teeth?

• Speed ratio = T_driven/T_driver
• Speed ratio = T_driver/T_driven in all cases
• Speed ratio = T_driver × T_driven
• Speed ratio = T_driver + T_driven

Explanation:

• For a simple gear pair, N_driverT_driver = N_drivenT_driven.
• Therefore, N_driver/N_driven = T_driven/T_driver.
• Thus, a larger driven gear rotates at a lower speed than the smaller driving gear.

A 20-tooth gear drives a 60-tooth gear. What is the speed ratio N_driver/N_driven?

• 3
• 1/3
• 2
• 4

Explanation:

• Speed ratio = T_driven/T_driver.
• Therefore, speed ratio = 60/20 = 3.
• If the 20-tooth gear rotates at 900 rpm, the 60-tooth gear rotates at 300 rpm.

Which gear tooth profile is most commonly used in modern power transmission?

• Involute profile
• Parabolic profile only
• Elliptical profile
• Circular arc profile only

Explanation:

• The involute profile is widely used because it provides a constant velocity ratio even when the centre distance changes slightly.
• It is comparatively easy to manufacture and maintain.

What is the main function of a governor?

• To regulate the mean speed of an engine according to load changes
• To store energy during an engine cycle
• To transmit power between shafts
• To reduce bearing friction

Explanation:

• A governor automatically adjusts the working-fluid or fuel supply as the load changes.
• Its purpose is to maintain the mean speed within a desired range.
• Flywheel and governor have different functions.

Which of the following is a centrifugal governor?

• Watt governor
• Dead-weight governor
• Pressure governor only
• Hydraulic accumulator

Explanation:

• The Watt governor is a centrifugal governor.
• Centrifugal governors operate using the centrifugal effect produced by rotating masses.
• Other examples include Porter and Proell governors.

In a centrifugal governor, the balls move outward when the engine speed:

• Increases
• Decreases to zero
• Remains exactly constant
• Becomes independent of load

Explanation:

• When speed increases, centrifugal force on the rotating balls increases.
• The balls move outward, causing the sleeve mechanism to move and reduce the fuel or working-fluid supply.
• This action tends to restore the engine speed.

What is a riveted joint?

• A permanent joint made by rivets to connect two or more plates
• A temporary joint made only by bolts
• A joint made only by welding
• A joint used only for gears

Explanation:

• Riveting is a permanent mechanical joining process.
• Rivets are inserted through holes in the plates and then deformed to form a head, securing the plates together.
• Riveted joints were historically common in boilers, bridges, tanks, and structural work.

Which type of riveted joint has the plates overlapping each other?

• Lap joint
• Butt joint
• Welded joint
• Flanged joint

Explanation:

• In a lap joint, one plate overlaps the other and the rivets pass through the overlapping portion.
• In a butt joint, the main plates are placed edge-to-edge and cover plates are generally used.

What is the primary function of a cam?

• To convert rotary motion into a prescribed reciprocating or oscillating motion
• To store electrical energy
• To increase fluid pressure
• To join two shafts permanently

Explanation:

• A cam is a rotating or sliding machine element that gives a follower a specified motion.
• Cams are widely used in engines, automatic machines, and control mechanisms.
• The shape of the cam profile determines the follower motion.

In a cam mechanism, the member that follows the cam profile is called the:

• Follower
• Crank
• Rocker
• Gear

Explanation:

• The follower remains in contact with the cam surface and moves according to the cam profile.
• Followers may be translating or oscillating and may have roller, flat-faced, or knife-edge contact.

Which type of follower has a roller at its contacting end?

• Roller follower
• Knife-edge follower
• Flat-faced follower
• Spherical follower only

Explanation:

• A roller follower uses a small roller to contact the cam.
• Rolling contact reduces sliding friction compared with a knife-edge follower and is widely used in high-speed mechanisms.

What is the main function of a bearing?

• To support a rotating shaft and reduce friction
• To increase shaft friction
• To store fuel
• To increase gear tooth pressure

Explanation:

• Bearings support rotating or moving machine elements while reducing friction and wear.
• They are broadly classified into sliding-contact and rolling-contact bearings.
• Ball and roller bearings are examples of rolling-contact bearings.

Which bearing primarily supports a radial load?

• Radial bearing
• Thrust bearing only
• Footstep bearing only
• Collar bearing only

Explanation:

• Radial bearings are designed mainly to support loads acting perpendicular to the shaft axis.
• Thrust bearings are designed mainly for loads acting along the shaft axis.

What is friction in a collar bearing?

• Friction between the collar and bearing surface due to axial load
• Friction between two gear teeth only
• Friction between belt and pulley only
• Friction in a fluid nozzle

Explanation:

• A collar bearing supports an axial or thrust load.
• Friction occurs between the rotating collar and the stationary bearing surface.
• The frictional torque depends on the load, coefficient of friction, and dimensions of the bearing surfaces.

Which type of bearing is used mainly to support an axial load on a vertical shaft?

• Footstep bearing
• Journal bearing
• Radial ball bearing only
• Needle bearing only

Explanation:

• A footstep bearing supports the lower end of a vertical shaft and carries axial load.
• The end of the shaft rests on the bearing surface.

For a flat collar bearing under uniform pressure, the frictional torque depends on:

• The dimensions of the collar, axial load, and coefficient of friction
• Only the shaft speed
• Only the density of the lubricant
• Only the shaft length

Explanation:

• For a collar bearing, frictional torque is obtained by integrating the friction force over the bearing area.
• For a single collar under uniform pressure, the frictional torque is commonly expressed as T = μWR_m, where μ is coefficient of friction, W is axial load, and R_m is mean radius.
• The exact expression for R_m depends on the assumed pressure distribution.

Which machine element is used to transmit motion between two shafts by means of toothed engagement?

• Gear
• Belt
• Clutch
• Bearing

Explanation:

• Gears transmit power through direct engagement of their teeth.
• Unlike friction belt drives, properly meshing gears provide a positive velocity ratio without normal slip.

Which device primarily absorbs and releases energy to smooth cyclic speed fluctuations?

• Flywheel
• Governor
• Clutch
• Gearbox

Explanation:

• The flywheel stores kinetic energy when the supplied torque exceeds the resisting torque and releases it when the supplied torque is insufficient.
• This action smooths the cyclic variation of shaft speed.

What happens to the speed of the driven shaft when a small gear drives a larger gear?

• The driven shaft rotates at a lower speed
• The driven shaft always rotates faster
• Both shafts must rotate at the same speed
• The driven shaft does not rotate

Explanation:

• For meshing gears, N₁T₁ = N₂T₂.
• If T₂ is larger than T₁, then N₂ is smaller than N₁.
• Thus, a larger driven gear provides speed reduction and torque multiplication, neglecting losses.