In the figure above, a box of mass 2.5kg is initially at rest on a rough inclined plane. Assuming the
mass is released and acquires a velocity of 4m/s at point P, the base of the incline. Find
A) The Work done against friction. (6 marks)
B) The Friction force.

Explanation:

By work - energy theorem on the box

Wmg + wn + wf = kf - ki

=> mgh + 0 + wf = 1/2 mv^2f - 1/2mv^2i

=> wf = 1/2mv^2f - 1/2mv^2i - mgh

:. Wf = 1/2×2.5×4^2 - 0- 2.5×9.8×1.5

= 20 - 36.75

= -16.75 J

Work done comes out negative here which is expected as the friction always act opposite to the velocity of an object. Friction is a non conservative force and it causes loss of mechanical energy.

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.

answer: good job it's all correct !

explanation: