An electron and a proton are moving under the influence of mutual forces. In calculating the change in the kinetic energy of the system during motion, one ignores the magnetic force of one on another. This is, because

A proton is kept at rest. A positively charged particle is released from rest at a distance $d$ in its field. Consider two experiments; one in which the charged particle is also a proton and in another, a positron. In the same time $$t$$, the work done on the two moving charged particles is

A man squatting on the ground gets straight up and stand. The force of reaction of ground on the man during the process is

A bicyclist comes to a skidding stop in 10 m . During this process, the force on the bicycle due to the road is 200 N and is directly opposed to the motion. The work done by the cycle on the road is

A body is falling freely under the action of gravity alone in vaccum. Which of the following quantities remain constant during the fall?