NEET-XII-Physics
08: Work and Energy
- #17Consider the situation of the previous question from a frame moving with a speed v0 parallel to the initial velocity of the block. (a) What are the initial and final kinetic energies? (b) What is the work done by the kinetic friction? (a) What are the initial and final kinetic energies? (b) What is the work done by the kinetic friction?Ans : The relative velocity of the ball w.r.t. the moving frame is given by `` {v}_{r}=v-{v}_{0}``. (a) Initial kinetic energy of the ball = `` \frac{1}{2}m{{v}_{r}}^{2}=\frac{1}{2}m(v-{v}_{0}{)}^{2}``
Also, final kinetic energy of the ball = `` \frac{1}{2}m(0-{v}_{0}{)}^{2}=\frac{1}{2}m{{v}_{0}}^{2}`` (b) Work done by the kinetic friction = final kinetic energy `` -`` initial kinetic energy
= `` \frac{1}{2}m({v}_{0}{)}^{2}-\frac{1}{2}m(v-{v}_{0}{)}^{2}``
= `` -\frac{1}{2}m{v}^{2}+mv{v}_{0}``
Page No 131: (a) Initial kinetic energy of the ball = `` \frac{1}{2}m{{v}_{r}}^{2}=\frac{1}{2}m(v-{v}_{0}{)}^{2}``
Also, final kinetic energy of the ball = `` \frac{1}{2}m(0-{v}_{0}{)}^{2}=\frac{1}{2}m{{v}_{0}}^{2}`` (b) Work done by the kinetic friction = final kinetic energy `` -`` initial kinetic energy
= `` \frac{1}{2}m({v}_{0}{)}^{2}-\frac{1}{2}m(v-{v}_{0}{)}^{2}``
= `` -\frac{1}{2}m{v}^{2}+mv{v}_{0}``
Page No 131:
- #17-aWhat are the initial and final kinetic energies?Ans : Initial kinetic energy of the ball = `` \frac{1}{2}m{{v}_{r}}^{2}=\frac{1}{2}m(v-{v}_{0}{)}^{2}``
Also, final kinetic energy of the ball = `` \frac{1}{2}m(0-{v}_{0}{)}^{2}=\frac{1}{2}m{{v}_{0}}^{2}``
- #17-bWhat is the work done by the kinetic friction?Ans : Work done by the kinetic friction = final kinetic energy `` -`` initial kinetic energy
= `` \frac{1}{2}m({v}_{0}{)}^{2}-\frac{1}{2}m(v-{v}_{0}{)}^{2}``
= `` -\frac{1}{2}m{v}^{2}+mv{v}_{0}``
Page No 131: