# Energy and Work Class-7th Goyal Brothers Physics Solutions Ch-3 Unit-1

Energy and Work Class-7th Goyal Brothers Physics Solutions Chapter-3. We Provide Step by Step Answers of Objective, True False , Fill in the blanks, Match the following , Study Questions of Chapter- 3 Energy , Unit-1(Energy And Work And Their Units) Visit official Website  for detail information about ICSE Board Class-7.

## Energy and Work Class-7th Goyal Brothers

Physics Solutions Chapter-3 Unit-1

 Board ICSE Class 7th Subject Physics Book Name Goyal Brothers Theme-3 Energy Unit-1 Energy And Their Work And Their Units Topic Solution of exercise questions Session 2023-24

### OBJECTIVE TYPE QUESTIONS

Physics Solutions Chapter-3 unit-1

#### A. Fill in the blanks :

1. The object which does work, _loses_ energy.
2. The object on which work is done, _gains_ energy.
3. A boy carrying a heavy school bag and standing still does _no_ work.
4. The work done by a body is the product of force and _displacement_.
5. _Calorie_ is the old unit of work.

#### B. Write ‘True’ or ‘False’ for the following statements :

1. An old unit of energy is calorie. [T]
2. The product of force and the displacement caused by it is called power. [F]
3. A student preparing his lessons for monthly tests does mental work. [F]
4. A boy carrying a school bag on his shoulder does work. [F]
5. If the displacement caused by a force is at right angles to the direction of applied force, the work done is zero. [T]

#### 1. Work is done when you hold a heavy suitcase in your hand.

Correct Statement: Work is done when you displace a heavy suitcase in your hand.

#### 2. Work done by a body is the product of power and displacement.

Correct Statement: Work done by a body is the product of force and displacement.

#### 3. Work is done when a force causes displacement at right angles to its own direction.

Correct Statement: Work is done when a force causes displacement at less than 90 degrees to its own direction.

#### 4. A teacher taking a class while standing, does work.

Correct Statement: A teacher taking a class while walking, does work.

#### 5. The SI unit of work or energy is calorie.

Correct Statement: The SI unit of work or energy is joule.

(a) Power

(b) efficiency

(c) energy

(d) force

Ans: (c) energy

(a) power

(b) energy

(c) force

(d) pressure

Ans: (c) force

(a) newton

(b) joule

(c) calorie

(d) newton-metre

Ans: (c) calorie

#### 4. 50 joules work is done, when a force ‘f’ causes a displacement of 10 m. The magnitude of force is :

(a) 5 pascal

(b) 5 newton

(c) 5 newton-metre

(d) none of these

Ans: (b) 5 newton

#### 5. When is the work done in the following situation :

1. A girl pushing a wall
2. A boy carrying a suitcase ibn h is hand.
3. A stone falling freely
4. A boy climbing up the stairs

(a) (i) and (ii)

(b) (i) and (iii)

(c) (ii) and (iv)

(d) (iii) and (iv)

Ans: (c) (ii) and (iv)

#### 4. work

Column A Column B

### STUDY QUESTIONS

#### (c) Is the energy spent on thinking or talking a kind of work? Give reason for your answer.

(a) It is nothing but a process of energy transfer to an object by applying force. Work is said to be done only if there is a displacement caused due to the force.

(b) The SI unit of work is joule (J). Joule is defined as the work done by a force of one newton causing a displacement of one meter. Sometimes, newton-metre (N-m) is also used for measuring work.

(c) When we talk or think our brain is working means our brain is doing mental work but there is no displacement in this process. Then we can say, there is no energy spent on thinking or talking.

#### (c) State two example when a force acting on a body does not do any work.

(a) The capacity to do work is called  Energy.

(b) Mathematically, the concept of work done W equals the force f times the distance (d), that is W = f * d

(c) If you push a wall and it doesn’t move, work is not done as there is no displacement. When we hold a bag on our head and walk horizontally such that the angle between the displacement and the gravitational force is , thus, work done is zero.

#### Question 3. The SI unit o f work or energy is joule. Explain why the work and energy have same SI unit.

Answer: The SI unit o f work or energy is joule and they have same SI unit because energy is the form of work that is stored and work is the one that is used. Therefore, work and energy, while not synonyms, are consistent with respect to the object. So they both have the same SI unit.

#### Question 4. A force of 15 N causes a displacement of 5 m in its own direction. What is the magnitude of work done?

Answer:  Work done = Force × Displacement

Given,  Force = 15 N

Displacement = 5 m

Therefore,

Work done = 15×5 = 75 J

The work done is 75 Joule.

#### Question 5. A body does a work 0f 1000 J in dragging a sack of rice through a distance of 20 m. What is the magnitude of force applied by the boy ?

Given,

Work done = 1000 J

Displacement = 10m

Therefore,
Work done= Force  Displacement

The magnitude of force applied by the boy is 50 N.

#### Question 6. A girl applies a force of 60 N in pushing a table, such that work done by her is 15 J. Calculate the displacement produced in the table.

Given,

Work done = 15 J

Force applied = 60 N

Therefore,
Work done= Force  Displacement

The displacement produced in the table is 0.25 m.

— : end of Energy and Work Class-7th Goyal Brothers Physics Solutions Chapter-3 :–-