Question

A load lorry mass 1200kg moves velocity of 12m/s its velocity become 10m/s after 5 second (a) what is the initial momentum and what is the final momentum .b) what is the change in momentum​

Answer 1

Given :

• Mass of lorry, m = 1200 kg
• Initial velocity, u = 12 m/s
• Final velocity, v = 10 m/s
• Time, t = 5 seconds

To find :

• Initial momentum
• Final momentum
• Change in momentum

According to the question,

a)

➞ Initial momentum = Mass × Initial velocity

➞ Initial momentum = 1200 kg × 12 m/s

➞ Initial momentum = 14400 kg m/s

• So, the initial momentum is 14400 kg m/s.

➞ Final momentum = Mass × Final velocity

➞ Final momentum = 1200 kg × 10

➞ Final momentum = 12000 kg m/s

• So, the final momentum is 12000 kg m/s.

b)

➞ Change in momentum = Final momentum - Initial momentum

➞ Change in momentum = 12000 - 14400

➞ Change in momentum = - 2400 kg m/s

• So,the change in momentum is 2400 kg m/s.

Answer 2

We have,

Mass of lorry = 1200 kg

Initial velocity = 12 m/s

Final velocity = 10 m/s

{Clearly, u > v. ⇒ There is a deceleration.}

(i) We know,

p = mv {in usual terms}

∴ p_intial = mu = (1200 kg)(12 m/s)

⇒ p_intial = 14400 kg m/s ...(I)

Similarly, p_final = mv

⇒ p_final = (1200 kg)(10 m/s)

⇒ p_final = 12000 kg m/s ...(II)

(ii) Change in momentum = mv - mu

{Do not confuse it with impulse.}

⇒ p_change = 12000 kg m/s - 14400 kg m/s

⇒ p_change = - 2400 kg m/s ...(III).