Class 7 Science Chapter 7 Motion, Force and Work Textbook Answers

Maharashtra Board Class 7 Science Solutions Chapter 7 Motion, Force and Work

Balbharti Maharashtra State Board Class 7 Science Solutions Chapter 7 Motion, Force and Work Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 7 Science Solutions Chapter 7 Motion, Force and Work

Class 7 Science Chapter 7 Motion, Force and Work Textbook Questions and Answers

Exercise

1. Fill ¡n the blanks with the proper words from the brackets.
(stationary, zero, changing, constant, displacement, velocity, speed. acceleration, stationary but not zero. inc reuses)

(a) If a body traverses a distance in direct proportion to the time, the speed of the body is ……………… .
Answer: constant

(b) If a body is moving with a constant velocity, its acceleration is ……………… .
Answer: zero

(d) …………….. is the distance traversed by a body in a particular direction in unit time.
Answer: Velocity

2. Observe the figure and answer the questions.

Sachin and Sarneer started on a motorbike from place A, took the turn at B, did a task at C, travelled by the route CD to D and then went on to E. Altogether, they took one hour for this journey. Find out the actual distance traversed by them and the displacement from A to E. From this, deduce their speed. What was their velocity from A to E in the direction AE’? Can this velocity be called average velocity?

Answer: 1. Actual distance = AB + BC + CD + DE = 3 + 4 + 5 + 3 = 15 km

2. Displacement = AB + BD + DE = 3 + 3 + 3 = 9 km

5. Yes, this velocity can be called as average velocity.

3. From the groups B and C, choose the proper words, for each of the words in group A.

Answer:

Group ‘A’	Group B’	Group ‘C’
Work	Joule	erg
Force	Newton	dyne
Displacement	Metre	cm

4. A bird sitting on a wire, flies, circles around and comes back to its perch. Explain the total distance it traversed during its flight and its eventual displacement.

Answer: The total distance the bird has traversed is the length of the distance covered by circling, but the displacement of the bird is zero as its initial and final position is the same.

5. Explain the following concepts in your own words with everyday examples : force, work, displacement, velocity, acceleration, distance.

Answer:

Force: Force is any energy that is exerted on a body to push or pull it, such that the body tends to change the state of rest or motion or change its shape.

e.g. a person lifting heavy object, an ox pulling a cart, etc.

Work: Work is the energy transfer from one object to another through force, making the object change position.

e.g. pulling a heavy box, an arrow releasing from a bow, drawing water from a well, etc.

Displacement: The minimum distance traversed by a moving body in one direction from the original point to reach the final point, is called displacement.

e.g. A car moving from one place to another.

Velocity: Velocity is the distance traversed by a body in a specific direction in unit time.

e.g. an athlete running 2 km in 15 mins.

Acceleration: The change in velocity per second is acceleration.

e.g. A football moving on a ground.

Distance: The length of the route actually traversed by a moving body, irrespective of the direction, is called distance.

e.g. a boy travelling one km from his home to school.

6. A ball is rolling from A to D on a flat and smooth surface. Its speed is 2 cm/s. On reaching B, it was pushed continuously up to C. On reaching D from C, its speed had become 4cm/s. It took 2 seconds for it to go from B to C. What is the acceleration of the ball as it goes from B to C ?

Answer:
Initial Velocity = 2 cm/s.
Final Velocity = 4 cm/s
Change in velocity: 4cm/s – 2 cm/s = 2 cm/s

Time taken for the change in velocity = 2 s

7. Solve the following problems.

(a) A force of 1000 N was applied to stop a car that was moving with a constant velocity. The car stopped after moving through 10m. How much is the work done?
Answer:
Force (F) = 1000 N
displacement (s) = 10m
work done (W) = ?
W = Fs
= 1000 × 10
W = 10,000 Joule

(b) A cart with mass 20 kg went 50 m in a straight line on a plain and smooth road when a force of 2 N was applied to it. How much work was done by the force?
Answer:
Force (F) = 2 N
Displacement (s) = 50 m
Work done (W) = ?
W = Fs
= 2 × 50
W = 100 Joule

Project :

Collect information about the study made by Sir Isaac Newton regarding force and acceleration and discuss it with your teacher.