You throw a ball straight down off the roof of a 47 m tall building with an initial velocity of -8m/s. When does the ball hit the ground?

t = 2.38 [s]

Explanation:

To solve this problem we must use the following equation of kinematics. We must clarify that both the acceleration and the initial velocity were taken as positive, since the velocity of the movement coincides with the direction of the acceleration.

where:

x - Xo = distance = 47 [m]

Vo = initial velocity = 8 [m/s]

a = gravity acceleration = 9.81 [m/s²]

t = time [s]

Now replacing these values in the equation:

47 = 8*t + 0.5*9.81*t²

47 = 8t + 4.905t²

47 = 4.905*t(1.63 + t)

9.58 = t*(1.63 + t) solving this equation (cuadratic)

we found that t = 2.38 [s]

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.

answer: the correct answer is 1.

explanation: there are various process in which a radioactive nuclei decays:

1) alpha decay: in this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. the mass number is reduced by 4 units.

2) electron capture: in this decay process, a parent nuclei absorbs an electron and gets converted into a neutron. simply, a proton and an electron combines together to form a neutron. mass number does not change in this process.

3) gamma ray emission: it is a decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. this decay releases . this process does not change the mass number.

4) positron emission: it is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. this is also known as -decay. in this the mass number remains same.

from the above information, we see that only alpha-decay is producing a change in the mass number of the nucleus.