Why does athlete pushes the earth backward fith his feet and hands just before the race starts

Is the portion of the electromagnetic spectrum that has a frequency just above that of visible light.

Find an expression for the electric field e⃗ at the center of the semicircle. hint: a small piece of arc length δs spans a small angle δθ=δs /r, where r is the radius. express your answer in terms of the variables q, l, unit vectors i^, j^, and appropriate constants.

How can a cyclist's acceleration change even if its velocity remains constant?