Physics problem

1.Birds resting on high-voltage power lines are a common sight. The copper wire on which a bird stands is 2.2cm in diameter and carries a current of 50A. If the bird's feet are 4.0cm apart, calculate the potential difference across its body. 2.An x-ray tube used for cancer therapy operates at 4.0MV, with a beam current of 25mA striking the metal target. Nearly all the power in this beam is transferred to a stream of water flowing through holes dirlled in the target. What rate of flow, in kilograms per second, is needed if the temperature rise(delta t) of the water is not to eceed 50degreesC? The answer is 0.48kg/s but not sure how to obtain this....

Understanding the concepts.

A) Very often a sinking ship will turn over as it becomes immersed in water. Why? B) Is it true that a floating object will only be in stable equilibrium if its centre of buoyancy lies above its centre of gravity? C) Why should one take short steps rather than long ones when walking on ice?

Calculating the specific temperature that balls will sink in benzene.

Benzene has a density of 0.90gm/cm^3 at 0 deg C and a coefficient of cubical expansion of 0.0012 per deg Celsius. Wooden balls (of density 0.88g/cm^3) therefore float in it at 0 deg Celsius. If the wood has a mean coefficient of linear expansion of 4 x 10^-5 per deg Celsius, calculate at what temperature the balls will just sink.

Calculating the temperature gradient in a bar whose one end is kept in ice and the other in steam.

A uniform copper bar 50 cm long is insulated on the sides and has its ends exposed to ice and steam respectively. If there is a layer of water 0.1 mm thick at each end, calculate the temperature gradient in the bar at steady state. Thermal conductivity of copper = 1.04 cgs units Thermal conductivity of water = 0.0014 cgs units.

Thermodynamics explanations

(1)Explain why a beaker filled with water at 4 degree celcius overflows if the temperature is decreased or increased (2)Mercury boils at a temperature of 357Degree Celcius. How then can mercury thermometers be used to measure temperatures up to 500 Deg Celcius ? (3)Two thermometers are constructed in the same way except that one has a spherical bulb and the other has a cylindrical bulb. whic one will respond quickly to temperature changes ?