A body constrained to move along the \(\mathrm{z}\)-axis of a coordinate system is subjected to constant force given by \(\vec{F}=-\hat{i}+2 \hat{j}+3 \hat{k}\) where \(\hat{i},\hat{j} \) and \(\hat{k}\) are unit vectors along the \(\mathrm{x}\)-axis, \(\mathrm{y}\)-axis and \(\mathrm{z}\)-axis of the system respectively. The work done by this force in moving the body a distance of \(4\) m along the \(\mathrm{z}\)-axis will be:
1. \(15\) J
2. \(14\) J
3. \(13\) J
4. \(12\) J
A body of mass 2 kg initially at rest moves under the action of an applied horizontal force of 7 N on a table with a coefficient of kinetic friction = 0.1. The work done by the applied force in 10 s is:
1. 882 J
2. 635 J
3. 247 J
4. 120 J
Which one of the following statement is wrong?
1. | When a conservative force does positive work on a body, the potential energy of the body decreases. |
2. | Work done by a body against friction always results in a loss of its kinetic energy. |
3. | The rate of change of the total momentum of a many-particle system is proportional to the sum of the internal forces on the system. |
4. | In an inelastic collision of two bodies, the total linear momentum of the system of two bodies does not change after the collision. |
An electron and a proton are detected in a cosmic ray experiment, the first with kinetic energy 10 keV, and the second with 100 keV. The ratio of their speeds is:
( = , = , 1 eV = ).
1. 13.5: 1
2. 1: 1
3. 1: 13.5
4. 2: 1