Question

Read the given passage and answer the questions based on the passage and related studied concepts.
Work done in science is much different from the conception of work in our daily life. We consider that work is being done by a clerk while sitting at one place from morning to evening. But in terms of physics, work is done only when an applied force produces a displacement in the body in its own direction. Work is a scalar quantity, but it can be negative, positive as well as zero.
1. A continuous force of 60 N acting on a box continuously, displaces it by 10 m in the direction of force. What is the work done?
2. Give two conditions of zero work done.
3. Give two examples of situations in which work done is negative.
4. Name the force which always does negative work on a body. Why does it do only negative work?
OBJECTIVE QUESTIONS:
1.When non-zero force and displacement are observed with zero work done, the angle between force and displacement is __________.
2.__________ work is done by a satellite revolving around the earth.
3.Work done can be __________, __________ or __________.
4. An athlete takes a round of a field and comes back to starting point, work done by athlete is __________.
5. A student studying hard for exam does more work than a baby crawling randomly from one corner of a room to another. [True/False]
6. Work done is a vector quantity. [True/False]
7. ASSERTION AND REASON QUESTIONS:
DIRECTIONS:
a. Assertion and reason are correct and reason is the correct explanation of assertion.
b. Assertion and reason are correct but reason is not the correct explanation of assertion.
c. Assertion is true but reason is false.
d. Assertion is false and reason is true.
e. Both assertion and reason are false.
(I) ASSERTION: We do not work while we push a wall.
REASON: The condition for a force to do the work is that it should produce motion in the object.
(II) ASSERTION: Work done by the force of friction is always negative.
REASON: Frictional force always acts in opposite direction to that of motion of
the body.
8. MULTIPLE CHOICE QUESTIONS:
(I) If 1 newton of force displaces a body by 1 m, the work done is
(i) 10 joule
(ii) 5 joule
(iii) 1 joule
(iv) Depends on time
(II) A man holds and displaces a 20 kg mass horizontally in his stretched hand.
(i) He does zero work against force of gravity
(ii) He does 200 joules of work per metre
(iii) The work done against gravity cannot be estimated but non-zero
(iv) The work done against gravity is equal to the muscular energy.
ANSWER THE FOLLOWING QUESTIONS:
ENGLISH
1
What is work done in Physics?
1
2 Read the following situations:
“Child A is preparing for exam in his study room at his table.
Child B climbs a tree several feet high on the ground.” Who
has done more work and why?
1
3 A student is writing a three hours science paper. How much
work is done by the student? Give reasons to your answer.
1
4 State the SI unit of work. 1
5 Express work mathematically. 1
6 Define the SI unit of work. 1
7 What would be the work done if
(a) force on the object is zero? (b) displacement of the
object is zero?
1
8 A 2 m high person is holding a 25 kg trunk on his head and
is standing at a roadways bus-terminus. How much work is
done by the person?
1
9 A bullock is pulling a cart and the cart moves. Name the
object which is doing work and the object on which work is
done.
1
10 A coolie is walking on a railway platform with a load of 30 kg
on his head. How much work is done by coolie?
1
11 State the conditions for zero work done. 1
12 When is the work done by a body positive? 1
13 When is the work done by a body negative? 1
14 Give an example of positive work. 1
15 Give an example of negative work. 1
16 How is ‘work’ done in day-to-day life different from its
scientific conception?
1
ENGLISH
17
Can there be displacement of an object in the absence of
force acting on it? Justify. 1
18. An object thrown at certain angle to the ground moves in
a curved path and falls back to the ground. The initial and
final points of the path of the object lie on the same horizontal
line. What is the work done by the force of gravity on the
object? 1
19. Mohina was sitting in her room and preparing for the
exam. She had planned to finish her syllabus by studying
whole night. By morning she accomplished the task,
but was very tired. She then packed her bag and went to
school.
(a) How much work was done by Mohina from Physics point of
view and why?
(b) In what form did energy of food get converted while
Mohina was studying?
2
20. An old coolie carries heavy luggage on his head at a railway
station. Manoj watches it from a distance and reaches to help
him out. They took the luggage at its place. The coolie thanks
Manoj for his help. Manoj asks him to be careful in future.
(a) What work was done by coolie on the luggage from
Physics point of view?
(b) Give reason for your reply in above question.

Answer 1

Answer:

1. work done = force × displacement

w = 60×10=600j

2. Two conditions when the work done is zero are: (i) When there is no displacement (S=0) and, (ii) When the displacement is normal to the direction of the force

3. (i) When a body is thrown upwards, gravity does the negative work. Since the gravitational force acts downwards but the displacement is upwards. (ii) When we walk frictional force does the negative work since frictional force acts opposite to displacement.

4. Gravity

objective:

1. 90 degrees
2. When a satellite moves around the Earth, then the force of gravity on the satellite is perpendicular to its displacement. Hence, the work done on the satellite by the Earth is zero.

positive, negative and zero

1. nection
2. true
3. false

ASSERTION AND REASON QUESTIONS

1. Both assertion and reason are false
2. Assertion is true, reason is false

. MULTIPLE CHOICE QUESTIONS:

1. c
2. He does zero work against force of gravity