Class 9 Work and Energy Important QuestionsImportant Questions Notes
Work and Energy Important Questions
- Define 1 watt of power.
- What is the commercial unit of energy. Convert it to the S.I. unit.
- Derive the formula for kinetic energy.
- State law of conservation of energy.
- Show that the total mechanical energy for a freely falling body remain constant/conserved.
- Calculate the total electricity bill amount for the month of April, if the following devices are used as follows:-
- 3 bulbs of 40 w for 6 hours
- 4 tube-light of 50 w for 8 hours
- A TV of 120 w for 6 hours.
Given the rate of electricity is ₹ 2.50 per unit.
- Where does an oscillating pendulum have maximum P.E. and K.E.?
- When a pendulum bob oscillates, why does the bob eventually come to rest? What happens to its energy?
- What are the differences between gravitational potential energy and elastic potential energy?
- When a ball is thrown inside a moving bus, does its kinetic energy depend on the speed of the bus?
- The work done by a force acting obliquely is given by the formula: W = F S Cos θ. What will happen to the work done if angle θ between direction of force and motion of the body is increased gradually? Will it increase, decrease or remain constant?
- A bullet of mass 15 kg has a speed of 400 m/s. What is its kinetic energy? If bullet strikes a thick target and is brought to rest in 2 cm, calculate the average net force acting on the bullet. What happens to the kinetic energy originally in the bullet.
- A ball is dropped from a height of 10 m. If the energy of the ball reduces by 40% after striking the ground, how much high can the ball bounce back? ( g = 10 m/s2 )
- Mathematically prove that the total mechanical energy for a freely falling body remains conserved.
- What will happen to the potential energy of a body when its height is doubled?
- Derive the relationship between kinetic energy and momentum.
- Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h.