A 7-cm-external-diameter, 18-m-long hot-water pipe at 80°C is losing heat to the surrounding air at 5°C by natural convection with a heat transfer coefficient of 25 W/m2·°C. Determine the rate of heat loss from the pipe by natural convection, in kW.

Explanation:

Given:

D = 7 cm

= 0.07 m

A = pi × r ^2

= pi × (0.07/2)^2

= 0.00385 m2

T1 = 80°C

T2 = 5°C

h = 25 W/m2·°C

Q = A × h × delta T

= 0.00385 × 25 × (80 - 5)

= 7.22 W

= 7.22 × 10^-3 kW.

b

explanation:

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.