Kwhen an observer is moving towards a stationary object making a sound, the pitch of the sound is perceived to be fluctuating higher unchanged lower

How many neutrons does element x if it’s atomic number is 28 and its mass number is 87

Beryl states that insulation with the smallest possible thermal conductivity is best to keep a house warm in winter, but worst for keeping a house cool in summer. sapphire insists the reverse is true: low thermal conductivity is good in the summer, but bad in the winter. which one, if either is correct? a. beryl, because low thermal conductivity results in low heat transfer. b. beryl, because low thermal conductivity results in high heat transfer. d. sapphire, because low thermal conductivity results in high heat transfer. e. neither, because low heat transfer is desirable both in summer and in winter.

What do we mean by the event horizon of a black hole?