Everything Science Grade 11

12.5 CHAPTER 12. FORCE,MOMENTUM AND IMPULSE

tum of the cricket ball.

SOLUTION

Step 1 : Identify what information is given and what isasked for

The question explicitly gives

• the mass of the ball (m = 160 g = 0,16 kg), and


• the velocity of the ball(v = 40 m·s−^1 )
  To calculate the momentum we will use

p = m· v

Step 2 : Do the calculation

p = m· v

= (0,16kg)(40m· s−^1 )

= 6,4kg· m· s−^1

= 6,4kg· m· s−^1 in the direction of the batsman

Example 28: Momentum of the Moon

QUESTION

The Moon is 384 400 km away from the Earth and orbits the Earth in 27,3 days. If the Moon

has a mass of 7,35 x 10^22 kg, what is the magnitude of its momentum if we assume a circular

orbit?

SOLUTION

Step 1 : Identify what information is given and what isasked for

The question explicitly gives

• the mass of the Moon(m = 7,35 x 10^22 kg)


• the distance to the Moon (384 400 km = 384400 000 m = 3,844 x 1 08 m)


• the time for one orbit of the Moon (27,3 days =27,3 x 24 x 60 x 60 = 2,36 x 10^6 s)
  We are asked to calculate only the magnitudeof the momentum of the
  Moon (i.e. we do not need to specify a direction). In order to do this werequire
  the mass and the magnitude of the velocity of the Moon, since

p = m· v

Step 2 : Find the magnitude ofthe velocity of the Moon