WORK, ENERGY & POWER

Other Chapters

• Q1: Define Work. State its unit.
  Ans: Work is said to be done when a force acts on a body and the body moves in the direction of force.
  
  Unit of work is Joule (J).
• Q2: Define Joule.
  Ans: One joule is the amount of work done when a force of 1 newton moves a body through a distance of 1 meter in the direction of force.
• Q3: Write the formula to calculate Work done.
  Ans: Work done formula:
  
  W = F × d × cosθ
• Q4: Define Energy. State its unit.
  Ans: Energy is the capacity to do work.
  
  Unit of energy is Joule (J).
• Q5: State the types of Energy.
  Ans: The types of energy are:

  • ➔ Kinetic energy
  • ➔ Potential energy
• Q6: Define Kinetic Energy.
  Ans: Kinetic energy is the energy possessed by a body due to its motion.
• Q7: Define Potential Energy.
  Ans: Potential energy is the energy possessed by a body due to its position or state.
• Q8: A car of mass 1200kg is moving with a velocity of 80 km/h. Find its kinetic energy.
  Ans: Given:
  Mass, m = 1200 kg
  Velocity, v = 80 km/h = (80 × 1000) / 3600 = 22.22 m/s
  
  Formula:
  KE = (1/2) m v²
  
  Step 1: Substitute values
  KE = (1/2) × 1200 × (22.22)²
  
  Step 2: Calculation
  KE = 600 × 493.7
  KE = 296220 J
  
  Final Answer:
  Kinetic Energy ≈ 2.96 × 10⁵ J
• Q9: State the Work Energy Relation.
  Ans: The work energy relation states that work done on a body is equal to the change in its kinetic energy.
• Q10: Define Power. State its Unit.
  Ans: Power is the rate of doing work or rate of transfer of energy.
  
  Unit of power is Watt (W).
• Q11: State the formula to calculate Power.
  Ans: Formula:
  
  P = W / t
• Q12: Define Watt.
  Ans: One watt is the power when 1 joule of work is done in 1 second.
• Q13: Define Horse Power.
  Ans: Horse power is a unit of power used in engineering.
  1 HP = 746 watts.
• Q14: State the Relation between Watt and Horse Power.
  Ans: 1 Horse Power = 746 Watts
• Q15: Define Indicated Horse Power (I.H.P).
  Ans: Indicated Horse Power is the power developed inside the cylinder of an engine.
• Q16: Define Brake Horse Power (B.H.P).
  Ans: Brake Horse Power is the actual power available at the output shaft of an engine.
• Q17: Define Dynamometer. Write its types.
  Ans: A dynamometer is a device used to measure power of an engine.
  
  Types:

  • ➔ Absorption dynamometer
  • ➔ Transmission dynamometer
• Q18: What is an Absorption Dynamometer?
  Ans: An absorption dynamometer absorbs the power produced by the engine and converts it into heat.
• Q19: What is a Transmission Dynamometer?
  Ans: A transmission dynamometer measures power while it is being transmitted from the engine to the load.
• Q20: What is a Prony Brake Dynamometer?
  Ans: A Prony brake dynamometer is an absorption type dynamometer used to measure engine power by friction braking.
• Q21: What is a Rope Brake Dynamometer?
  Ans: A rope brake dynamometer is a device in which power is absorbed by a rope wrapped around a pulley.
• Q22: State the uses of a Dynamometer.
  Ans: The uses of a dynamometer are:

  • ➔ Measuring engine power
  • ➔ Testing machine performance
  • ➔ Laboratory experiments
• Q23: Define Power Loss.
  Ans: Power loss is the difference between input power and output power of a machine.
• Q24: Write the formula to find I.H.P of an engine.
  Ans: Formula:
  
  I.H.P = (P × L × A × N) / 4500
  
  where:
  P = pressure
  L = stroke length
  A = area
  N = number of strokes
• Q25: Find work in Joules done by a motor of 5 hp in 2 hours.
  Ans: Given:
  Power = 5 HP
  Time = 2 hours
  
  Step 1: Convert HP to Watt
  1 HP = 746 W
  P = 5 × 746 = 3730 W
  
  Step 2: Convert time to seconds
  t = 2 × 3600 = 7200 s
  
  Step 3: Work formula
  W = P × t
  
  Step 4: Calculation
  W = 3730 × 7200
  W = 26856000 J
  
  Final Answer:
  Work done = 2.6856 × 10⁷ J
• Q26: Define Efficiency.
  Ans: Efficiency is the ratio of useful output power to input power expressed in percentage.
  
  Formula:
  
  η = (Output / Input) × 100%
• Q27: Describe the relationship between I.H.P, B.H.P and Efficiency.
  Ans: Efficiency is given by:
  
  η = (B.H.P / I.H.P) × 100%
  
  It shows how much input power is converted into useful output power.