- Force
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- Law's Of motion
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- First Law of Motion
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- Momentum
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- Second Law of Motion
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- Third Law of Motion
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- Law Of conservation of Momentum

Given a=4.00 m/s

=1000kg

F= 4000 N

If you apply a net force of 3 N on .1 kg-box, what is the acceleration of the box

(a) 2 m/s

(b) 30 m/s

(c) 10 m/s

(d) None of these.

Acceleration is given by a=change in velocity/Time taken

So a=1 m/s

Now force is given by

F=ma

F=1 N

S.No |
time |
Momentum |
Velocity |

1 |
1sec |
||

2 |
1.5 sec |
||

3 |
2 sec |
||

4 |
2.5 sec |

Velocity can find using

V=u+at

u=0

v=at

omentum

P=mV

S.No |
time |
Momentum |
Velocity |

1 |
1sec |
20 Kg m/s |
2 m/ |

2 |
1.5 sec |
30 kg m/s |
3 m/s |

3 |
2 sec |
40 kg m/s |
4 m/s |

4 |
2.5 sec |
50 kg m/s |
5 m/s |

a) 0 s

b) 2.23 s

c) 3.47 s

d) 4.57 s

A sedan car of mass 200kg is moving with a certain velocity . It is brought to rest by the application of brakes, within a distance o f 20m when the average resistance being offered to it is 500N.What was the velocity of the motor car?

Average acceleration= 500/200=-2.5 m/s

Now

v

Now v=0

So u=10 m/s

A driver accelerates his car first at the rate of 4 m/s

(a) 0 N

(b) 5 N

(c) 10 N

(d)20 N

A cricket ball of mass 0.20 kg is moving with a velocity of 1.2m/s . Find the impulse on the ball and average force applied by the player if he is able to stop the ball in 0.10s??

Impulse= Change in momentum= .20 X1.2=.12 Kgm/s

Fxt=.12

F=.12/.10=1.2 N

A car start from rest and acquire a velocity of 54 km/h in 2 sec. Find (i) the acceleration (ii) distance travelled by car assume motion of car is uniform iii) If the mass of the car is 1000 Kg,what is the force acting on it?

a) Acceleration is given by

a=(change in velocity)/Time taken

So a=7.5 m/s

b) Distance is given by

s=ut+(1/2)at

c) F=ma=1000X7.5=7500 N

A hockey ball of mass .2 Kg travelling at 10 ms

?P= m (v - u) = 0.2 (-2 - 10) = –2.4 kg ms

(The negative sign indicates a change in direction of hockey ball after it is struck by hockey stick. )

Two objects of masses of 100 gm and 200 gm are moving in along the same line and direction with velocities of 2 ms

u

By the law of conservation of momentum,

0.1 x 2+ 0.23 x 1=0.1 x 1.67 + 0.2 v

v

It will move in the same direction after collision

Anand leaves his house at 8.30 a.m. for his school. The school is 2 km away and classes start at 9.00 a.m. If he walks at a speed of 3 km/h for the first kilometer, at what speed should he walk the second kilometer to reach just in time?

An object of mass 1kg acquires a speed of 10 m/s when pushed forward. What is the impulse given to the object?

Impluse=Change in Momentum= 10 Kgm/s

A bullet of mass 10 gm is fired with an initial velocity of 20 m/s from a rifle of mass 4 kg. Calculate the initial recoil velocity of the rifle..

From law of conservation of Momentum

0=.01X20+4v

Or v=.05 m/s

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Class 9 Maths Class 9 Science