Ask Your Teacher A 51-kg pole vaulter running at 11 m/s vaults over the bar. Her speed when she is above the bar is 1.1 m/s. Neglect air resistance, as well as any energy absorbed by the pole, and determine her altitude as she crosses the bar.

6.11 N

Explanation:

Let,

m= mass of vaulter

Vi initial speed =11 m/s

Vf speed on pole (final) =1.1 m/s

Yi = initial height (when on ground)=o m

Yf = Height while crossing the pole =?

This problem can be solved by using conservation of energy rule;

KEi + PEi = KEf + PEf

==> 1/2 m+ mg = 1/2 m +mg

Initially the altitude of vaulter is zero i-e ==> PEi = mg = mg×0=0

==>1/2 m= /2 m +mg

==> m=m +2mg

cancelling m

==> = +2g

==> - =2g

==> =

==> =

==>  ==6.11N

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.