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Mechanical Engineering

Mechanics: Efficiency of the Machine

A machine is supplied energy at a rate of 4,000 W and does useful work at a rate of 3,760 W. What is the efficiency of the machine? a. 92 percent b. 94 percent c. 96 percent d. 97 percent?

Question about Multipal choice question on mechanics

A car with a mass of 2,000. kilograms is moving around a circular curve at a uniform velocity of 25 meters per second. The curve has a radius of 80 meters. What is the centripetal force on the car? a. 625 N b. 703N c. 15,625 N d. 20,250 N

Apparent Density, Theoretical Density and Void Volume

A compacted body of iron powder is sintered into a 20mm-diameter, 45-mm-tall cylinder which, upon weighing, is found to have a mass of 98g. Calculate the apparent density, the percentage of theoretical density, and the void volume (porosity) in percent.

Tensile stress

A bar of steel 1 by 1½ in cross section and 6 in long is subjected to a pull of 6000 lb. What is the average tensile stress in the bar?

Brayton Cycle Gas Turbines

Large stationary brayton cycly gas turbine power plant delivers a powr output of 100MW to an electric generator . Minimum temperature is 300K so T1= 300k max temp is 1600k so T3= 1600k Minimum pressure in the cycle is 100kpa compressor pressure ratio is 14 to 1 so p2/p1 = 14 but turbine efficiency is 85% and compressor efficienc

Mobility and transit time

Consider the 2.0micrometer long GaAs device where the E-field is 5kV/cm and Mn*=.067M0. (a) Calculate the transit time of an electron through the device if the mobility is 8000 cm^2V-s. (b) The mean free path of an electron (average velocity x scattering time) is the average distance an electron travels between two consecu

Excess carrier concentrations and diffusion current density.

Consider a bar of p-Si that is homogeneously doped to a value of 3x10^15 at T=300K. The applied electric field is zero. A light source is incident on the end of the semiconductor. The excess-carrier concentration generated at x=0 is deltap(0)=deltan(0)=10^13/cm^3. Neglect surface effects. Mun=1200/cm^2/Vs. Mup=400/cm^2/Vs.

Quasi Fermi Level

Q. An n-type silicon sample with Nd=10^16cm-3 is steadily illuminated such that g'=10^21cm-s^-1. If tn0=tp0=10^-6s, calculate the position of the quasi-Fermi levels for electrons and holes with respect to the intrinsic level (assume that ni=1.5x10^10cm^-3).

Barrage Energy Example

The area of morecambe bar at high water is approx. 200km^2. At low water most of the bay is exposed sand. for this exercise, we could assume that on average the sand slopes evenly so that half way between high and low tide the area of water is 100km^2. The tidal range (between low and high tide) varies between 4m at neap tide

Difficulty over a problem relating to the motion of a projectile.

A player throws a ball with an initial velocity Vo of 15 m/s from a point A located 1.5 m above the floor. Knowing that the ceiling of the gymnasium is 6 m high, determine the highest point B at which the ball can strike the wall 18 m away. This problem was taken from the curvilinear motion of particles inside the kinematics

Representative velocity profiles

Womersly’s Problem: Plot some representative velocity profiles for the purely oscillatory flow of a Newtonian fluid in a long, rigid, straight pipe at various phases of the flow (3-4). For these plots, use the values of constants given below: Constants: Velocity (u): 105 cm/s Diamter (d): 2.23 cm Kinematic viscosit

Rankine Cycles

Consider an ideal steam reheat and regenerative cycle where steam leaves a steam gen and enters a high pressure turbine at 3 Mpa and T=400 C and is extracted to an open feedwater heater at 0.8 Mpa. The remainder is reheated to 400 C at this pressure which flows to the low pressure turbine stage. The condenser saturation pressure

Diesel engine

A diesel engine has air before compression at 280 K and 85 Kpa. The highest temperature is 2219 K and the highest pressure is 6 MPa. Find the volumetric compression ratio and the mean effective pressure using cold air properties at 300K.

Thin walled box beam with end load at an angle.

A box beam made from an extruded aluminium ally having 5 414 mm wall thickness is loaded by an inclined force P=100 N, as shown in the figure. Determine the maximum stress on section a-b. For the box beam, use the centreline dimension for finding I. (Note that the stress is far away from the support where large local stress co

Hollow shaft transmitting power with shear limits.

(a) Design a hollow steel shaft to transmit 300 hp at 75 rpm without exceeding a shear tress of 8000 psi. Use 1.2:1 as the ratio of the outside diameter to the inside diameter. (b) What solid shaft could be used instead?