Mechanical Engineering Answers

A turbine shaft of diameter 250 mm is running at 1600 r.p.m. in a journal bearing and supports a load of 130 kN. Calculate (a) length of bearing if the permissible bearing pressure is 1.5 N/mm2 , (b) coefficient of friction, (c) rubbing velocity, (d) amount of heat to be removed by the lubricant per minute. The bearing temperature is 58 °C and viscosity of oil at this term is 0.02 kg/m-s. The bearing clearance is 0.25 mm, k = 0.002.

When the cold junction of a thermocouple thermometer is at 0oC and the hot junction at 100

oC, the millivoltmeter shows a deflection of 4.2 mV towards the left. The cold junction is now

put in an unknown temperature while maintaining the hot junction at 100oC. The

millivoltmeter now shows a deflection of 5.2 mV towards the right. Calculate the unknown

temperature

An endless belt 4 m long passes over a pulley of 300 mm diameter making 80 rev/minute. The pulley accelerates to 240 rev/minute in 40 seconds. If there is no belt slip, calculate:

7.1 the angular acceleration of the pulley and the linear acceleration of the belt.

7.2 the number of revolutions made by the pulley during its acceleration.

7.3 the number of times a point on the belt will pass over the pulley in 12 seconds.

Also clearly show the values of the following:

ω1

ω2

α

a

θ

ω2

θ

s

times

A 320 mm diameter-grinding wheel must be driven at a peripheral grinding speed of 1200 meters/min. It takes 62 seconds to reach this speed from rest, runs at this speed for the following two and a half minutes and then begins to decelerate uniformly, coming to rest after a further 10 seconds. Draw a neat angular velocity/time graph and use it to determine how many revolutions the wheel made since starting from rest.

Also clearly show what the following values are

v

ω

θ1

θ2

θ3

θtotal

1.1 The speed of a shaft increases from 93 r/min to 305 r/min with an angular acceleration of 2,4 rad/s2. How many revolutions does the shaft make during the first 3 seconds of acceleration? How many revolutions does the shaft make in the last 4.25seconds. Show all calculations[10]

1.2 A motor that runs at 1240 rev/minute is required to drive a belt at 20 m/s. What diameter belt pulley is required?[3]

Also clearly show the following values:

ωi

ωf

θ

r

d

ωf

A 350 mm diameter grinding wheel must be driven at a grinding speed (speed at circumference) if 1200 meters per minute. It takes 5 seconds to reach this speed from rest, runs at this speed for the next two minutes and then starts to decelerate uniformly, finally coming to rest after a further 30 seconds. Draw a neat angular velocity-time graph and determine how many revolutions the wheel made in total.

Also clearly show what the following values are:

ω1

θ1

θ2

θ3

θtotal

A pulley (A) diameter 300mm is accelerated by means of a belt drive from 60rpm to 240rpm during 360 revolutions. Attached by means of a belt is another pulley (B), with diameter 200mm. Calculate:

a)The angular acceleration of each pulley

b)The initial and final velocity of the smaller pulley (B) in rad/s

Also

Clearly show the values of the following:

Pulley A-ωi

Pulley A-ωf

Pulley A-αA

Pulley B-αB

Pulley B-ωi

Pulley B-ωf

A jet fighter aircraft is climbing vertically ay 120m/s when it releases a bomb that hits the ground 35seconds later. How high was the jet when the bomb was released?

A hovercraft stays off the ground by blowing air out underneath it. It can accelerate (forwards or backwards) at 0,6 m/s² by blowing air with a steering fan (backwards or forwards). If the hovercraft is moving forwards at 12 m/s and the steering fan is suddenly turned to accelerate the hovercraft backwards, calculate:

a) the velocity of the hovercraft after 2 s

b) the time it takes for the hovercraft to reach zero velocity 

c) the velocity of the hovercraft after 29 s

d) the displacement of the craft when it has zero velocity

e) the displacement of the hovercraft when it is moving backwards at 16m/s

f) Clearly show what the value of h(max),t(total) and v

State whether the hovercraft is going backwards or forwards after each question’s answer.

(Make forward direction positive and backwards direction negative)