Building A and B are 99m apart. A student stands at P, so that his distance from building A is 33m. After clapping his hands once, he hears several echoes. The speed of sound in air is 330m/s
Calculate the time interval between clapping his hands and hearing.
1) the first echo = ?
2) the third echo =?​

when insulating materials rub against each other, they may become electrically charged . electrons , which are negatively charged, may be 'rubbed off' one material and on to the other. the material that gains electrons becomes negatively charged. the material that loses electrons is left with a positive charge.

the device is called “ rocket engine”

find the surface area of the sphere to the nearest square unit. use a calculator.

a. 254 in.2

b. 64 in.2

c. 127 in.2

d. 1,018 in.2