Calculating Momentum of a Puck with Given Velocity and Mass

[zaraox]

A puck has a velocity of 3i –4j m/s and a mass of 20 kilograms. What is the momentum of the puck?

A. 100 Ns
B. 60i – 4j Ns
C. 60i – 80j Ns
D. 23i – 24j Ns

Alright, so I calculated the velocity from the resultant vector to be 5 m/s. So:

p = mv
p = 20 kg x 5 m/s
p = 100 Ns

But I can also do this:

p = mv
p = 20(3i - 4j)
p = 60i - 80j Ns

So what answer is right, A or C?

 

[collinsmark]

Hello zaraox,

Welcome to Physics Forums!

Momentum is a vector (it is not a scalar quantity). That means momentum has both magnitude and direction. Which one of your approaches preserves this property?

 

[zaraox]

Hello zaraox,

Welcome to Physics Forums!

Momentum is a vector (it is not a scalar quantity). That means momentum has both magnitude and direction. Which one of your approaches preserves this property?

So the answer would be C then? :)

 

[collinsmark]

So the answer would be C then? :)

Sounds good to me.

 

[zaraox]

Haha, embarrassingly simple. Thank you!