Class XI

Physically, the notion of potential energy is applicable only to
  1. The class of forces where work done against the force gets converted to thermal energy
  2. The class of forces where work done against the force gets converted to kinetic energy
  3. The class of forces where work done against the force gets stored up as energy.
  4. The class of forces where work done against the force gets dissipated
kWh is the unit of
  1. acceleration
  2. work
  3. power
  4. Energy
A bullet of mass 0.012 kg and horizontal speed 70 m s−1s−1 strikes a block of wood of mass 0.4 kg and instantly comes to rest with respect to the block. The block is suspended from the ceiling by means of thin wires. Calculate the height to which the block rises. Also, estimate the amount of heat produced in the block.
  1. 29.2 cm, 29.5 J
  2. 72.2 cm, 28.5 J
  3. 21.2 cm, 28.5 J
  4. 23.2 cm, 38.5 J
A 6.0-kg block initially at rest is pulled to the right along a horizontal, surface having a coefficient of kinetic friction of 0.15, by a constant horizontal force of 12 N. Find the speed of the block after it has moved 3.0 m.
  1. 0.8 m/s
  2. 3.8 m/s
  3. 2.8 m/s
  4. 1.8 m/s
In which case is the work done zero ?
  1. Force and displacement are perpendicular to each other
  2. Force and displacement are at an angle of 45∘
  3. Force and displacement are in the same direction
  4. Force and displacement are at an angle of 75∘
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