How Is Impulse Calculated in Volleyball?

[ravirodrigues]

Homework Statement

Items A and B :)

Relevant Equations

F~ = (260N)ˆi − (180N)ˆj
v~ = (15m/s)ˆi−(8m/s)j

In a volleyball match a player hits a 280g mass ball with a force given by

. A force acts for 4 meters and the ball acquires a final velocity given by

. (a) What is the momentum the player has applied to ball? (b) What is the final speed of the ball?

Thank you.

 

[haruspex]

Homework Statement:: Items A and B :)
Homework Equations:: F~ = (260N)ˆi − (180N)ˆj
v~ = (15m/s)ˆi−(8m/s)j

In a volleyball match a player hits a 280g mass ball with a force given by View attachment 254050. A force acts for 4 meters and the ball acquires a final velocity given by View attachment 254051 . (a) What is the momentum the player has applied to ball? (b) What is the final speed of the ball?

Thank you.

Per forum rules, you need to post an attempt.

 

[Cutter Ketch]

The force acts for 4 meters! Them are some loooonnggg arms!

 

[hyunxu]

For finding momentum, you can use the formulaP=mv
For finding final velocity , you can use , the kinematic equation v^2 = u^2+ 2as
and to find that a , use a = f ÷m

 

[haruspex]

For finding momentum, you can use the formulaP=mv
For finding final velocity , you can use , the kinematic equation v^2 = u^2+ 2as
and to find that a , use a = f ÷m

I think you mean, to find the initial velocity, u. The final velocity is given.
And the appropriate momentum formula is $\Delta p=m(v-u)$.

 

[lightlightsup]

Are you supposed to assume that the initial velocity was 0?

 

[haruspex]

Are you supposed to assume that the initial velocity was 0?

No, it can be calculated from the given information. In fact, I wonder if part b) is supposed to ask for that; seems a bit trivial to ask for the final speed when the final velocity is a given.

 

[lightlightsup]

Part (b) is trivial: Just calculate the magnitude of the given $\vec{v_f}$.
For Part (a): I keep getting a negative under the square root.
If I assume that the volleyball is being served and therefore starting at a velocity of 0, it becomes easier?
Aren't you assuming that the displacement is completely in the direction of the force?
Something isn't working out for me here.

 

[haruspex]

Part (b) is trivial: Just calculate the magnitude of the given →vfvf→.
For Part (a): I keep getting a negative under the square root.
If I assume that the volleyball is being served and therefore starting at a velocity of 0, it becomes easier?
Aren't you assuming that the displacement is completely in the direction of the force?
Something isn't working out for me here.

As @Cutter Ketch pointed out in post #2, the 4m is clearly wrong, but @ravirodrigues has not come back to correct it. Probably should be 4cm. Or even 4mm.
Taking the initial velocity as zero doesn't help.

If the displacement is not in the direction of the force we do not have enough info for part a unless we do take the initial velocity as zero, but then we don't need F or the 4m.

 

[lightlightsup]

As @Cutter Ketch pointed out in post #2, the 4m is clearly wrong, but @ravirodrigues has not come back to correct it. Probably should be 4cm. Or even 4mm.

With 4cm, the math does workout.

 

[hyunxu]

I think you mean, to find the initial velocity, u. The final velocity is given.
And the appropriate momentum formula is $\Delta p=m(v-u)$.

We can consider the ball to be in rest initially so the initial velocity will be zero.

 

[haruspex]

We can consider the ball to be in rest initially

How so? It doesn't say this is the serve.
Also, please see last para in post #9.

 

[hyunxu]

How so? It doesn't say this is the serve.
Also, please see last para in post #9.

Yes , you're right!