The sun continuously radiates energy into space in all directions. Some of the sun's energy is intercepted by the Earth. The average temperature of the surface of the Earth remains a little above 300 k. Why doesn't the Earth's temperature rise as it intercepts the sun's energy?

A. The Earth reflects the sun's light.

B. The Earth radiates an amount of energy into space equal to the amount it receives.

C. The energy only raises the temperature of the upper atmosphere and never reaches the surface.

D. The thermal conductivity of the Earth is low.

E. The heat is carried away from the Earth by convection currents.

In a system, when potential energy decreases, then entropy also decreases. true false

The frequency of vibrations of a vibrating violin string is given by f = 1 2l t ρ where l is the length of the string, t is its tension, and ρ is its linear density.† (a) find the rate of change of the frequency with respect to the following. (i) the length (when t and ρ are constant) (ii) the tension (when l and ρ are constant) (iii) the linear density (when l and t are constant) (b) the pitch of a note (how high or low the note sounds) is determined by the frequency f. (the higher the frequency, the higher the pitch.) use the signs of the derivatives in part (a) to determine what happens to the pitch of a note for the following. (i) when the effective length of a string is decreased by placing a finger on the string so a shorter portion of the string vibrates df dl 0 and l is ⇒ f is ⇒ (ii) when the tension is increased by turning a tuning peg df dt 0 and t is ⇒ f is ⇒ (iii) when the linear density is increased by switching to another string df dρ 0 and ρ is ⇒ f is ⇒

Física: un futbolista patea hacia el arco con una velocidad de 15m/ah, calcular: a)el alcance para un ángulo de tiro de 25º, b) el tiempo que el balón permanece en el aire.