Four forces of the same magnitude but differing directions act at and tangent to the rim of a uniform wheel free to spin about its center of mass (CM). Which statement about the wheel is correct?
A. None of these
B. Neither the net force on the wheel nor the net torque on the wheel about the CM
is zero.
C. The net force on the wheel is not zero but the net torque about the CM is zero.
D. The net force on the wheel and the net torque on the wheel about the CM are zero.
E. The net force on the wheel is zero but the net torque about the CM is not zero.

Explanation:

Four forces of the same magnitude with different directions may not be able to cancel each other .

But of they are applied in opposite directions they can cancel each other also . Because the exact point of application of the forces are not given . Thus we can not say any thing about the resultant forces .

Thus option ( a ) can be taken as correct .

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.

object 2 because all the other ones are wrong