General Science Solutions Solutions for Class 7 Science Chapter 7 - Motion, Force And Work

Answer:

(a) If a body traverses a distance in direct proportion to the time, the speed of the body is constant.
(b) If a body is moving with a constant velocity its acceleration is zero.
(c) Speed is a scalar quantity.
(d) Velocity is the distance traversed by a body in a particular direction in unit time.

Answer:

Actual distance travelled by Sachin and Sameer from A to E = AB + BC + CD + DE = 3 + 4 + 5 + 3 = 15 km
Displacement from A to E = AB + BD + DE = 3 + 3 + 3 = 9 km
$\mathrm{Speed} \mathrm{of} \mathrm{the} \mathrm{motorbike} \mathrm{from} \mathrm{A} \mathrm{to} \mathrm{E}=\frac{\mathrm{Total} \mathrm{distance} \mathrm{travelled} \mathrm{from} \mathrm{A} \mathrm{to} \mathrm{E}}{\mathrm{Total} \mathrm{time} \mathrm{taken} \mathrm{from} \mathrm{A} \mathrm{to} \mathrm{E}}=\frac{15}{1}=15 \mathrm{km}/\mathrm{h}$
$\mathrm{Velocity} \mathrm{of} \mathrm{the} \mathrm{motorbike} \mathrm{from} \mathrm{A} \mathrm{to} \mathrm{E}=\frac{\mathrm{Total} \mathrm{displacement} \mathrm{from} \mathrm{A} \mathrm{to} \mathrm{E}}{\mathrm{Total} \mathrm{time} \mathrm{taken} \mathrm{from} \mathrm{A} \mathrm{to} \mathrm{E}}=\frac{9}{1}=9 \mathrm{km}/\mathrm{h}$
Yes, this can be called the average velocity of the motorbike from A to E.

Answer:

Answer:

The total distance travelled by the bird during its flight = 2$\times$(Distance between the point where the bird was sitting and the point from where it takes a turn)
The eventual displacement of the bird is zero as it returns to its initial point i.e. where it was sitting.

Answer:

Force: It is any kind of push or pull on a body due to another body when the bodies interact with each other. It is a vector quantity. For example, a person applies a force in the form of push or pull to open a door.

Work: It is defined as the work done by a force that causes a displacement in an object. It is a scalar quantity. For example, a child does work when he drags a toy car on the ground.

Displacement: It is the shortest distance between the initial and final position of an object. It is a vector quantity. For example, when we go to a mall for shopping from our house and then return to the house, the displacement would be 0 as our initial position (house) and final position (house) is same.

Velocity: Velocity is defined as the rate of change of displacement. It is a vector quantity. For example, a car running on a straight road has some velocity.

Acceleration: The rate of change of velocity is known as acceleration. It is a vector quantity. For example, if a car is moving on a straight with variable speed, it will posses some acceleration. In case the speed of the car remains same but the direction of car changes, then also the car would be accelerating.

Distance: It is the actual path length covered by an object during its motion. It is a scalar quantity.  For example, when we go to a mall for shopping from our house and then return to the house, the distance travelled by us would be twice the distance between our house and the mall.

Answer:

The acceleration of the ball between A to B is zero as the speed and direction of the ball is constant. After point B, a force is applied. Thus, the ball will get accelerated.
$$\begin{gathered} \mathrm{Acceleration} \mathrm{of} \mathrm{the} \mathrm{ball} \mathrm{from} \mathrm{B} \mathrm{to} \mathrm{C}=\frac{\mathrm{Change} \mathrm{in} \mathrm{velocity} \mathrm{from} \mathrm{B} \mathrm{to} \mathrm{C}}{\mathrm{Time} \mathrm{taken} \mathrm{for} \mathrm{this} \mathrm{change}} \\ \mathrm{Acceleration} \mathrm{of} \mathrm{the} \mathrm{ball} \mathrm{from} \mathrm{B} \mathrm{to} \mathrm{C}=\frac{4-2}{2}=1 \mathrm{m}/{\mathrm{s}}^2 \end{gathered}$$

Answer:

(a) $\mathrm{Work} \mathrm{done} \mathrm{by} \mathrm{the} \mathrm{force} \mathrm{to} \mathrm{stop} \mathrm{the} \mathrm{car}=F\times S=1000\times 10=10000 \mathrm{J}$

(b) $\mathrm{Work} \mathrm{done} \mathrm{by} \mathrm{the} \mathrm{force}=F\times S=2\times 50=100 \mathrm{J}$