FORCE and MOTION

FORCE and MOTION

DIFFERENCE BETWEEN

1.      Distance and displacement.

Distance	Displacement
a)      It is the actual length of the path traveled by a body.	a)      It is the shortest distance between any two points.
b)      It is a scalar quantity.	b)      It is a vector quantity.

2.      Centripetal force and centrifugal force.

Centripetal Force	Centrifugal Force
a)      It pulls the body towards the center.	a)      It pushes the body away from the center.
b)      E.g.- a revolution of the earth around the sun.	b)      E.g.- tied stone escaped from a rope.

3.      Speed and velocity

Speed	Velocity
a)      It is the distance per unit of time.	a)      It is the displacement per unit of time.
b)      It is a scalar quantity.	b)      It is a vector quantity.

4.      Velocity and acceleration.

Velocity	Acceleration
a)      It is the distance covered in a straight line.	a)      It is the rate of change of velocity.
b)      Its unit is m/s.	b)      Its unit is m/s2.

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GIVE REASONS

1.      The atmosphere is surrounding the earth.

Answer: The atmosphere is surrounding the earth it is due to the gravity of the earth.

2.      Ball bearings are used on the wheels of bicycles.

Answer: Ball bearings are used on the wheels of bicycles to reduce friction.

3.      We reduce friction in machines.

Answer: We reduce friction in machines to increase the efficiency (output) of the machines.

4.      Groves and ridges are made in the tires of vehicles.

Answer: Groves and ridges are made in the tires of vehicles to produce friction which prevents them from slipping.

5.      We may slip in a muddy path.

Answer: We may slip in a muddy path because in a muddy path there is no friction.

6.      Usually value of velocity is lesser than that of speed.

Answer: Since Velocity is the measure of displacement and it is the shortest path so the velocity is always lesser than that of speed.

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ANSWER QUESTIONS

1.      What is force? Also, write its unit.

Answer: Force is a push or pull that changes or tries to change the state of a body from rest to motion or motion to rest. Its SI unit is Newton.

2.      Write any four effects of force.

Answer: Four effects of force are as follows

a)      Force can move an object.

b)      Force can stop a moving object.

c)      Force can make a moving object change its speed.

d)      Force can change the shape of an object.

3.      Define magnetic force and gravitational force with suitable examples.

Answer: The force which attracts the magnetic substance is called magnetic force. Examples are iron, cobalt, nickel, etc.

The force of attraction between any two bodies is called gravitational force. Examples are stone, water, and fruits. etc.

4.      How can we reduce friction?

Answer: We can reduce friction through lubricants, and ball bearings and make the sliding surface smooth.

5.      Define acceleration. Also, give its unit.

Answer: The rate of change of velocity is called acceleration.

Its unit is m/s²

6.      Define speed and velocity. Also, write their units.

Answer: The distance covered per unit time is called speed. Its unit is m/s.

The displacement per unit of time is called velocity. Its unit is m/s.

7.      What are distance and displacement?

Answer: The actual length of the path is called distance.

The shortest path between two points is called displacement.

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SOLVE [MATHEMATICAL PROBLEMS]

1.      A body of mass 14kg is moving with an acceleration of 5 m/s^2. Calculate the force applied to the body.

Solution: Given,

Mass (M) = 14kg

Acceleration (A) = 5m/s² 

Force (F) =?

We know,

Force (F) = M x A

=14 x 5

=70 N

There for, The force applied to the body is 70 N.

2.      A force of 30 N is applied to a body of mass 6kg. Calculate the acceleration produced on the body.

Solution: Given,

Mass (M) = 6kg

Acceleration (A) =? 

Force (F) = 30 N

We know,

Force (F) = Mass (M)

= F / M

= 30N / 6kg

= 5m/s²

There for, The acceleration produced on a body is 5m/s².

3.      A body is moving with an acceleration of 60 m/s². If the force applied to the body is 42000 N, calculate its mass.

Solution: Given,

Mass (M) =?

Acceleration (A) = 60 m/s²

Force (F) = 42000 N

We know,

Mass (M) = F / A

= 42000 / 60

= 700 KG

There for, the Mass is 700 kg.

4.      Durga is running on the road. She covered a 2 km distance in 20 minutes. What is her average speed?

Solution: We have,

Distance (d) = 2km

Time is taken (t) = 20 min

Average speed =?

We know,

Average speed = d/t

= 2km / 20m

= 2 x 1000 m / 20 x 60 sec

= 2000/1200

= 5/3

= 1.67 m/s

There for, her average speed is 1.67 m/s.

5.     Birat starts running a straight path he reaches the destination of 90 meters in 0.5 minutes. Calculate his velocity.

Solution: Given,

Distance traveled (d) = 90m

Time is taken (t) = 0.5m

0.5 x 60 sec

30 sec

Initial Velocity (V) = 0

Final Velocity = 90m

Or, d/t = 90/30

Or, 3 m/s

There for, Velocity is 3 m/s.

6.      A car starts moving from rest. If it gains a velocity of 72 km/hr after 10 seconds, what is the acceleration of the car?

Solution: Given,

Initial Velocity (v) = 0m

Final Velocity (V) = 12km/hr

12 x 1000 / 60 x 60

720/30

20m/s

Again,

Time is taken (T) = 10sec

We have,

A= v-V/t 

A = 20-0/10

A = 2m/s²

There for, The acceleration of the car is 2m/s²

7.      A truck is running at a velocity of 90 km/hr. If it takes 5 seconds to stop, calculate the retardation of the car.

Solution: Given,

Initial velocity (V) = 90m/s

90 x 1000 / 60 x 60

900 / 36

25m/s

Again,

Final velocity (V) = 0

Time is taken (t) = 5 sec

We have,

A = v-u / t

A = 0 – 25 / 5

A = -5 m/s²

There for, retardation of the car is 5 m/s²

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