(a) what is the intensity in w/m2 of a laser beam used to burn away cancerous tissue that, when 90.0% absorbed, puts 500 j of energy into a circular spot 2.00 mm in diameter in 4.00 s

The intensity of a laser beam : 4.42.10⁷ W/m²

The energy transferred by waves per unit area per unit time is called wave intensity  

Because energy per unit time is Power, the intensity of the wave is equal to Power divided by area  

P = power, watt

W = energy, J  

t = time, s  

For waves that spread in all directions, the intensity at the distance R from the source can be formulated  

From the equation above shows the intensity of the wave is inversely proportional to the square of the distance from the source.  

The farther the wave spreads, the smaller the intensity  

Cancerous tissue area:

So that the intensity

electric field

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magnetism

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An electric device delivers a current of 5 a to a device.

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i think it's 35 meters

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.