Một con lắc là xo treo thẳng đứng có độ cứng 30 N/m và vật nặng có khối lượng 320 g. Kích thích dễ cho quá nặng dao động điều hoà theo phương thẳng đứng xung quanh vị trí cân bằng với biên độ 6 cm. Lấy g = 10m/s. Độ lớn lực kéo lớn nhất của là xa liễn điểm treo trong quá trình quả nặng dao động là

Glass is transparent to visibile light under normal conditions; however, at extremely high intensities, glass will absorb most of the light incident upon it. this works through a process known as multiphoton absorption. in this process, several photons are absorbed at the same time. if very intense light whose photons carry 2ev of energy is shined onto a material with a band gap of 4ev, that light can be absorbed through two-photon absorption, because two photons have the right amount of energy to bridge the band gap. what is the minimum number of photons of 800-nm light that are needed to equal or exceed the band gap of fused silica glass

The transfer of heat through the movement of a gas or liquid a. convection b. conduction c. radiation

Alead ball is dropped into a lake from a diving board 5m above the water . it hits the water with a certain velocity and then sink with constant velocity in bottom . it reaches the bottom 5 second after it is dropped if g= 10m/s2 . find depth of the lake and average velocity of the ball ?