Physics Answers

an ideal heat engine has an efficiency of 25% when its low temperature reserver is 25°C. it is desire to increase the efficiency to 35%. what change should be made in either (1) the temperature of the low reserver or (2) the temperature of the high reserver??

The internal energy of the certain substance is given by the following equation

u = 3.56 pv + 184

where u is given in kJ/kg, p is in kPa and v is in m3

/kg.

A system composed of 3 kg of this substance expands from an initial pressure of 500

kPa and volume of 0.22 m3

to final pressure 100 kPa in a process in which pressure and

volume are related by pv1.2 = Constant. If expansion is quasi-static, find Q, ∆U and W

for the process.

when a box of mass 4.5kg is given in an initial speed of 5m/s, it slides along horizontal flooor to a distance of 3m before coming to rest. what is the co-effiicient of the kinetic friction between the box and the floor?

9.The electric motor of a model train accelerates the train from rest to 0.620m/s in 21s. The 

total mass of the train is 875g. Find the average power delivered to the train during the 

acceleration? 

An ideal Stirling engine with air as the working fluid operates between specified pressure limits. The heat added to the cycle and the network produced by the cycle is to be determined.

Assumptions: Air is an ideal gas with constant specific heats. Properties: The properties of air at room temperature are R = 0.287 kPa·m3 /kg.K, cp = 1.005 kJ/kg·K, cv = 0.718 kJ/kg·K, and k = 1.4 

An ideal Stirling engine with air as the working fluid is considered. The temperature of the source-energy reservoir, the amount of air contained in the engine, and the maximum air pressure during the cycle are to be determined.

Assumptions: Air is an ideal gas with constant specific heats. Properties: The properties of air at room temperature are R = 0.3704 psia·ft3 /lbm.R, cp = 0.240 Btu/lbm·R, cv = 0.171 Btu/lbm·R, and k = 1.4.

An ideal Stirling engine using helium as the working fluid operates between temperature limits of 300 and 2000 K and pressure limits of 150 kPa and 3 MPa. Assuming the mass of the helium used in the cycle is 0.12 kg, determine (a) the thermal efficiency of the cycle, (b) the amount of heat transfer in the regenerator, and (c) the work output per cycle.

An air-standard cycle is executed in a closed system and is composed of the following four processes:

1-2 Isentropic compression from 100 kPa and 27°C to 1 MPa

2-3 P = constant heat addition in the amount of 2800 kJ/kg

3-4 v = constant heat rejection to 100 kPa

4-1 P = constant heat rejection to initial state

(a) Show the cycle on P-v and T-s diagrams.

(b) Calculate the maximum temperature in the cycle.

(c) Determine the thermal efficiency.

Assume constant specific heats at room temperature.

An 800 ft ship has a displacement of 35,000 tons, and the

area defined by the waterline is 38,000 ft2

. Will the ship take

more or less draft when steaming from salt water to fresh water?

How much will it settle or rise?

A 734 kg car is stuck on a road, 990 kg is traveling at 12 m/s to the east collides with the rear side of the car which is stuck on the road. In your role as an expert witness, you inspect the scene and determine that, after the collision, the 734 kg car slides on the road at 5 m/s in a direction 30 degrees north of east. Ignoring the effects of friction during the collision, calculate the magnitude of the velocity (in m/s) of the 990 kg car after the collision