At what distance does a 100 watt lightbulb deliver the same power per unit surface area as a 75 watt lightbulb produces 10 m away from the bulb? (assume both have the same efficiency for converting electrical energy in the circuit into emitted electromagnetic recall that watts = joules/second = power = energy per unit time. assume that the power of the electromagnetic waves spreads uniformly in all directions (i. e. spreads out over the area of a sphere) and use the formula for the surface area of a sphere.

Air is held within a frictionless piston-cylinder container, which is oriented vertically. the mass of the piston is 0.45 kg and the cross-sectional area is 0.0030 m2. initially (state 1) the pressure of the gas is sufficient to support the weight of the piston as well as the force exerted by the atmospheric pressure ( 101.32 kpa). the volume occupied by the air within the cylinder in state 1 is 1.00 liter. one end of a spring (with spring constant k = 1000 n/m) is attached to the top of the piston, while the other end of the spring is attached to a stage that can move vertically. initially the spring is undeflected and therefore exerts no force. then the stage is then moved quasistatically downward a distance of 10.0 cm, at which point the system reaches state 2. the piston-cylinder is not insulated; rather it remains in diathermal contact with the surroundings, which are at a constant temperature of 300 k. what is the change of pressure within the container?

Atoms containing radioactive nuclei are called

How long will it take a car traveling of a constant speed of 45m/s to cover the distance of a 2.5km?