Class XI

A person trying to lose weight (dieter) lifts a 10 kg mass, one thousand times, to a height of 0.5 m each time. Assume that the potential energy lost each time she lowers the mass is dissipated. How much work does she do against the gravitational force ?
  1. 59000 J
  2. 49000 J
  3. 45000 J
  4. 55000 J
In which of the following cases is the work done positive?
  1. Work done by gravitational force while a man in lifts a bucket out of a well by means of a rope tied to the bucket
  2. work done by an applied force on a body moving on a rough horizontal plane with uniform velocity
  3. Work done by friction on a body sliding down an inclined plane
  4. Work done by the resistive force of air on a vibrating pendulum in bringing it to rest.
mass and energy are equivalent and are related by
  1. E = mc2
  2. E = 2mc2
  3. E = mc2/2
  4. E = mc3
The total mechanical energy of a system is conserved if the
  1. forces, doing work on it, are viscous
  2. forces, doing work on it, are damped
  3. forces, doing work on it, are conservative
  4. forces, doing work on it, are not conservative
How many joules of energy does a 100-watt light bulb use per hour? How fast would a 70-kg person have to run to have that amount of kinetic energy?
  1. 360000 J, 101 m/s
  2. 320000 J, 130 m/s
  3. 380000 J, 120 m/s
  4. 340000 J, 140 m/s
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