CBSE-XI-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?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}``
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- #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}``
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