Chapter 11. Work and Energy

Class 9 Science Examplar Chapter 11. Work and Energy Choose the correct answers :

Q1. Which of the following  statement is correct for ‘‘work done ’’ ?

(i) A donkey is carrying a load on its back .

(ii)  Suma is swimming in a pond .

(iii) A sailboat is moving due to wind energy .

(iv) A green plant is carrying out photosynthesis .

(A)  (i) and (iv)

(B) (ii) and (iv)

(C) (i) and (iii)

(D) (ii) and (iii)

Ans :  (D) (ii) and (iii)

Q2. Certain force acting on a 20 kg mass changes its velocity from 5 m/s to 2 m/s ,then the work done by the force is :

(A) 180 J

(B) 210 J

(C) 220 J

(D) 230 J

Ans : (B) 210 J

[Here,

We have,

 

 J

The negative sign means that work has been done in slowing the body ]

Q3.    is equal to –

(A)    J

(B)   J

(C)   J

(D)   J

Ans :  (D)   J

Q4. Work done on an object by a force would be zero if the displacement of the object is .

(A)  One

(B) Equal

(C) Zero

(D) none

Ans : (C) Zero

Q5. If an object of mass 10 kg when it is at a height of 6 m above the ground , then the potential energy is [Given,    ] :

(A)  590 J

(B) 580 J

(C) 588 J

(D) 688 J

Ans : (C) 588 J

[ Here,  

We have,  J ]

Q6. A lamp consumes 1000 J of electrical energy in 10s ,then its power is :

(A)  200 watt

(B) 100 watt

(C) 120 watt

(D) 210 watt

Ans : (B) 100 watt

[ Here,  J ,  

We have,  watt ]

Q7. The velocity of a body is double its kinetic energy :

(A) Becomes 4 times

(B) Does not change

(C) Becomes 2 times

(D) Becomes half

Ans :  (A) Becomes 4 times .

Q8. If an agent does a work W in time ,then power is   , then the unit of power becomes :

(A) kilowatt /hrs

(B) watt

(C) joule

(D) Joule/second

Ans : (B) watt

Q9. An object of mass 15 kg is moving with a uniform velocity of 4 m/s , then the kinetic energy possessed by the object is :

(A) 120 J

(B) 110 J

(C) 130 J

(D) 100 J

Ans : (A) 120 J

[Here,  

 J ]

Q10. An electric heater is rate 1500 W . How much energy does it use in 10 hours ?

(A)  15 J

(B) 30 J

(C) 45 J

(D) 10 J

Ans : (A) 15 J

[ Here, P = 1500 w = 1.5 kw , t = 10

We have,     J ]

Q11. When a body falls freely towards the earth, then its total energy :

(A) increases

(B) decreases

(C) remains constant

(D) first increases and then decreases

Ans : (C) remains constant .

Q12. A car is accelerated on a leveled road and attains a velocity 4 times of its initial velocity . In this process the potential energy of the car :

(A) does not change .

(B) becomes twice to that of initial

(C) becomes 4 times that initial

(D) becomes 16 times that of initial

Ans : (A) does not change .

Q13. In case of negative work the angle between the force and displacement is :

(A) 0°          

(B) 45°       

(C) 90°    

(d) 180°

Ans : (d) 180°

Q14. An iron sphere of mass 10 kg has the same diameter as an aluminium sphere of mass is 3.5 kg . Both spheres are dropped simultaneously from a tower . When they are 10 m above the ground ,

they have the same :

(A) Acceleration

(B) Momenta

(C) Potential energy

(D) kinetic energy

Ans : (A) Acceleration .

Q15. A girl is carrying a school bag of 3 kg mass on her back and moves 200 m on a leveled road . The work done against the gravitational force will be (  ) :

(A)   J

(B) 6 J

(C) 0.6 J

(D) zero

Ans : (D) zero

Q16. Which one of the following is not the unit of energy ?

(A) joule

(B) newton metre

(C) kilowatt

(D) kilowatt hour

Ans : (C) kilowatt .

Q17. The work done on an object does not depend upon the :

(A) displacement

(B) force applied

(C) angle between force and displacement

(D) initial velocity of the object

Ans : (D) initial velocity of the object .

Q18. Water stored in a dam possesses :

(A) no energy

(B) electrical energy

(C) kinetic energy

(D) potential energy

Ans : (D) potential energy .

Q19. A body is falling from a height . After it has fallen a height   , it will possess :

(A) only potential energy

(B) only kinetic energy

(C) half potential and kinetic energy

(D) more kinetic and less potential energy

Ans : (C) half potential and kinetic energy .

Q20. A man does 60 J of work in 6 seconds , then the Power is :

(A) 12 watts

(B) 10 watts

(C) 15 watts

(D) 36 watts

Ans : (B) 10 watts .

[ Power   watts ]  

Q21. A body posses potential energy 460 J whose mass is 20 kg and is raised to a certain height , then the height is [  ] :

(A) 3.2 m

(B) 2.2 m

(C) 2.3 m

(D) 3.5 m

Ans : (C) 2.3 m

[we have ,       m ]

Class 9 Science Examplar Chapter 11. Work and Energy Fill in the blanks :

Q22. Work done on an object by a force would be zero if the displacement of the object is  .

Ans : zero .

Q23.   is defined as the rate of doing work .

Ans : Power .

Q24. The energy used in one hour at the rate of  is called  .

Ans :   .

Q25. The sum of the kinetic and potential energies of an object is called its  .

Ans : mechanical energy .

Q26. The energy possessed by a body due to its change in position or shape is called the  .

Ans : potential energy .