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M2 Unequal impulse on the wall and the ball ? Is there a mistake in this textbook?

Good afternoon,

I am completely baffled by an example given in the textbook, shown below. I was hoping somebody could help me understand what is happening here.

First of all, I am assuming there should actually be a minus where I've marked it? Otherwise the answer is not even close to correct.

Second of all, why do they ignore the mass in the final answer and just write (0, 18sin75*). But then include the mass again when it comes to the impulse on the ball.

We then move on to calculating the impulse on the plane and the mass of the ball is ignored again. To make things even more confusing they clearly say "equal and opposite" and yet give the value 17.4 Ns which is clearly not equal to 3.48 Ns. What is going on here?

Thank you in advance for your time and help.

(edited 6 years ago)

Reply 1

ghostwalker

Original post by DeadManProp

First of all, I am assuming there should actually be a minus where I've marked it? Otherwise the answer is not even close to correct.

The given answer is clearly gibberish.

Yes, there should be a minus sign there.

Second of all, why do they ignore the mass in the final answer and just write (0, 18sin75*). But then include the mass again when it comes to the impulse on the ball.

Another error. There should be "0.2 x" in front of that vector.

We then move on to calculating the impulse on the plane and the mass of the ball is ignored again. To make things even more confusing they clearly say "equal and opposite" and yet give the value 17.4 Ns which is clearly not equal to 3.48 Ns. What is going on here?

And yet again. Impulse exerted on the plane is 3.48 Ns, not 17.4 Ns.

Not surprised you're confused by it.

Reply 2

RDKGames

Study Forum Helper

Original post by DeadManProp

Good afternoon,

I am completely baffled by an example given in the textbook, shown below. I was hoping somebody could help me understand what is happening here.

First of all, I am assuming there should actually be a minus where I've marked it? Otherwise the answer is not even close to correct.

That's right. The vertical velocity before impact

-12 \sin 75

Second of all, why do they ignore the mass in the final answer and just write (0, 18sin75*). But then include the mass again when it comes to the impulse on the ball.