Numerical Problems | Chapter 6 | Work & Energy | 9th Physics | National Book Foundation

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The unit of work or energy joule (j) is equal to
(a) horsepower (b) watt metre (c) watt second (d) newton second
A car, an elephant and a cricket ball have same kinetic energies. Which of these will have a greater speed?
(a) car (b) elephant (c) cricket ball (d) all have same speed
A ball weighing 50N is lifted to a height of 5 metre. The potential energy stored in it is:
(a) 10J (b) 25J (c) 45J (d) 55J
What is the power utilized when 100J of work is done in 5s.
(a) 10W (b) 20W (c) 105W (d) 500W
The SI unit of power is
(a) joule (b) watt (c) horsepower (d) erg
A 4kg body is thrown vertically upward from the ground with a velocity of 5m/s. If friction is neglected its kinetic energy just before hitting the ground is
(a) 25J (b) 50J (c) 75J (d) 100J
A ball is thrown downward with an initial velocity, its
(a) E_K increases & E_P decreases (b) E_K decreases & E_P increases
(c) Both E_K & E_P increases (d) Both E_K & E_P decreases
The type of energy derived from heated ground water is:
(a) tidal energy (b) geothermal energy (c) hydroelectric energy (d) nuclear energy
A weight lifter of power 1960 watt lifts a load of mass ‘M’ from the ground to a height of 2m in 3 second. ‘M’ is:
(a) 100kg (b) 200kg (c) 300kg (d) 400kg
Which one is renewable source of:
(a) Coal (b) Natural gas (c) sunlight (d) Uranium
One unit of horsepower is equivalent to:
(a) 756 watt (b) 716 watt (c) 736 watt (d) 746 watt
A practical engine cannot have an efficiency equal to greater than:
(a) 0 (b) 0.5 (c) 0.8 (d) 1
A heavy and a lighter object have same momenta. The object with greater kinetic energy is:
(a) lighter (b) heavy (c) same kinetic energy (d) either a or b
A force is acting on body but causes displacement. The work done on the body is
(a) positive (b) negative (c) zero (d) infinite
A box is taken to the second floor of a building by doing some work. This work converts to
(a) kinetic energy (b) potential energy (c) heat energy (d) sound energy
A car is moving with a constant speed along a straight road. Is there any work done on the car?
Does the work done in raising a box up in a building depend upon how fast it is raised up? Through which path? To how much height?
Work done on the body either speeds it up, slows it down. Keeping it mind, explain how much work is done by centripetal force on an orbiting satellite?
A car has kinetic energy E_K. By what factor its kinetic energy would change, if its velocity is doubled?
A bullet is fired from gun, bullet penetrates into sand wall and it stops. Where does its kinetic energy used?
An LED light bulb has efficiency of 80%. Does it violate conservation of energy principle?
How does using renewable energy sources contribute to reducing environmental impact compared to non-renewable sources?
Will we eventually rely entirely on renewable energy sources? Why or why not?
How can increasing the power of a machine impact its energy consumption?
A perpetual engine has an efficiency equal to 1. Why it will not work?
Calculate the work done in pushing a box with 150N through distance of 5m.
A boy weighing 75N jumps up and gains 300J of gravitational potential energy. Find the height to which the boy will rise.
A 5kg steel ball is dropped from the top of a 12m high tower. What is kinetic energy of the ball on hitting the ground? With what velocity will it hit the ground? (Neglect resistance).
A 2.0kg rock is dropped from 20m tall building. What is the kinetic and gravitational potential energy when the rock has fallen 15m.
A rocket with a mass of 800g is launched vertically upward with an initial speed of 30m/s. (a) Assuming no air resistance, calculate the maximum height the rocket would reach. (b) If, due to air friction, the rocket only rises to 25m, determine the work done against air resistance.
A 2hp electric motor gives energy to a system that lifts a load of 100kg to height of 10m in 1.5s. Calculate (a) Input (Work done by motor on system) (b) Output (load lifted by system) and (c) Efficiency of the system.
What horsepower (hp) is required to pump up 2500kg of water to 100m height in 5 minutes?