Class 10 (Science Assignment)

Force and Motion

Force is a push or pull that can change the state of rest or motion of an object. The SI unit of force is newton (N). According to Newton’s second law of motion, the force acting on an object is equal to the product of its mass and acceleration:

$$F = ma$$

where $F$ is force, $m$ is mass, and $a$ is acceleration.

Motion describes the change in position of an object with time. The distance travelled by an object is the total length of its path, while displacement is the shortest distance between its initial and final positions in a particular direction. Speed is the distance travelled per unit time, whereas velocity is displacement per unit time. Acceleration is the rate of change of velocity with time.

When an object moves with uniform acceleration, the following equations of motion can be used:

$$v = u + at$$ $$s = ut + \frac{1}{2}at^2$$ $$v^2 = u^2 + 2as$$

Here, $u$ is initial velocity, $v$ is final velocity, $a$ is acceleration, $t$ is time, and $s$ is displacement.

Newton's first law states that an object remains at rest or continues to move with uniform velocity in a straight line unless an external unbalanced force acts on it. This property of an object is called inertia. Newton's third law states that every action has an equal and opposite reaction. For example, when a person jumps from a boat onto a bank, the boat moves backward because of the reaction force.

Understanding force and motion helps us explain many everyday phenomena, such as the movement of vehicles, falling objects, jumping, walking, and the operation of machines.

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A. Short-Answer Questions

1. What is force? Write its SI unit.
2. State Newton's second law of motion and write its mathematical expression.
3. Differentiate between distance and displacement.
4. What is inertia? Give one example from daily life.
5. State Newton's third law of motion and give one suitable example.

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B. Multiple-Choice Questions

1. Which of the following is the SI unit of force?

a) Joule
b) Watt
c) Newton
d) Pascal

2. According to Newton's second law, force is equal to:

a) $m/a$
b) $ma$
c) $m+a$
d) $a/m$

3. Which quantity has both magnitude and direction?

a) Distance
b) Speed
c) Mass
d) Velocity

4. A body continues in its state of rest unless an external unbalanced force acts on it. This is explained by:

a) Newton's first law
b) Newton's second law
c) Newton's third law
d) Law of gravitation

5. When a person jumps from a boat to the shore, the boat moves backward. This is an example of:

a) Inertia
b) Newton's second law
c) Newton's third law
d) Uniform motion

C. Numerical Questions

1. Force and Acceleration

A body of mass 5 kg is acted upon by a force of 20 N. Calculate its acceleration.

$$a=\frac{F}{m}=\frac{20}{5}=\boxed{4\,m/s^2}$$

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2. Final Velocity

A car starts from rest and accelerates uniformly at 2 m/s² for 10 seconds. Calculate its final velocity.

$$v=0+(2\times10)=\boxed{20\,m/s}$$

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3. Distance Travelled

A motorcycle has an initial velocity of 5 m/s and accelerates at 3 m/s² for 4 seconds. Calculate the distance travelled.

$$s=20+24=\boxed{44\,m}$$

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4. Finding Acceleration

A train increases its velocity from 10 m/s to 30 m/s in 5 seconds. Calculate its acceleration.

$$a=\frac{30-10}{5} =\boxed{4\,m/s^2}$$

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5. Using $v^2=u^2+2as$

A car travelling at 10 m/s accelerates uniformly at 2 m/s² and covers a distance of 100 m. Calculate its final velocity.