The Momentum Questions And Solutions

The physics lesson, momentum subject. The momentum of an object that going with speed of V. Calculation of the momentum. Relationship between mass, velocity and momentum. Questions and answers.


Question -1

An object has a mass of 10 kg and a velocity of 20 m/s. This object hits a barrier and go back with velocity of 15 m/s.

What is the change in momentum of this object?


Solution:

The change in momentum of the object is found as follows.

ΔP = Plast – Pfirst

The momentum of the body is

P1 = 10•20 = 200 N•s

The momentum of the body is

P2 = -10•15 = -150 N•s

ΔP = P2 – P1

ΔP = -150 – 200 

= - 350 N•s


The sign of the result is negative (-), because the direction of the object is reversed. The magnitude of change in the momentum of the object is 350 N•s.


Question -2

A vehicle is travelling at velocity of 25 m/s.

This vehicle increase its velocity to 32 m/s after a while.

Mass of the vehicle is 500 kg.

Find the change in the momentum of the vehicle.


Solution:

First velocity of the vehicle is

V1 = 25 m/s

Last velocity of the vehicle is

V2  = 32 m/s

Mass of the vehicle is

m = 500 kg

First momentum of the vehicle is

P1 = 25•500

P1 = 12500 N•s

Last momentum of the vehicle is

P2 = 32•500

P2 = 16000

Change in the momentum is

ΔP = P2 – P1

ΔP = 16000 – 12500

ΔP = 3500 N•s


Question -3

A car that is motionless is starting travel and its velocity is being 30 m/s after a while.

The mass of the car is 800 kg.

Find the change in the momentum of the car.


Solution:

First velocity of the car is

V1 = 0 m/s

Last velocity of the car is

V2 = 30 m/s

The mass is

m = 800 kg


First momentum of the car is

P1 = 0•800 = 0

Last momentum of the car is

P2 = 30•800 = 24000

The change in the momentum of the car is

ΔP = 24000 – 0

= 24000 N•s


Question -4

moment_T1I1


The body in the figure is moving toward the barrier at a velocity of 15 m/s. The body is hits the barrier and going back at a velocity of 12 m/s as in the figure .

The mass of the body is 15 kg.

Find the change in the momentum of the body.


(sin37 = 0,6, sin53 = 0,8)


Solution:

moment_T1I2


We must find perpendicular components of the velocities of the object to the barrier . Then, we multiplication these velocities by the mass.

The perpendicular component of the V1 to the barrier is.

V1x = 0.6 V1

V1x = 15•0.6

V1x = 9 m/s

First momentum is

P1 = m•V1x

P1 = 15•9

P1 = 135 N•s


The perpendicular component of the V2 is

V2x = 0.8V2

V2x = 12•0.8

V2x = 9.6 m/s

The last momentum is

P2 = 15•9.6 

P2 = -144 N•s


ΔP = -144 – 135

ΔP = -279 N•s

ΔP = 279 N•s


Question -5

moment_T1I3


The velocity-time graph of an object K is as in the figure.

The mass of the object K is 12 kg.

What is the change in momentum of the object between 0 and 8 seconds?


Solution:

The velocity of the object is 15 m/s instant of t=0 . The velocity of the object was increases to 27 m/s after 27 second. The change in the velocity is 12 m/s.


P1 = 15•12 = 180 N•s

P2 = 27•12 = 324 N•s


ΔP = Plast – Pfirst

ΔP = 324 – 180

ΔP = 144 N•s





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February 14 2019

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