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# Though most tennis players generally strive to strike the ba

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Though most tennis players generally strive to strike the ba [#permalink]  26 Oct 2017, 06:25
Expert's post
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Question Stats:

62% (07:29) correct 37% (09:56) wrong based on 8 sessions

Though most tennis players generally strive to strike the ball on the racket's vibration node, more commonly known as the “sweet spot,” many players are unaware of the existence of a second, lesser-known location on the racket face, the center of percussion, that will also greatly diminish the strain on a player's arm when the ball is struck.

In order to understand the physics of this second sweet spot, it is helpful to consider what would happen to a tennis racket in the moments after impact with the ball if the player's hand were to vanish at the moment of impact. The impact of the ball would cause the racket to bounce backwards, experiencing a translational motion away from the ball. The tendency of this motion would be to jerk all parts of the racket, including the end of its handle, backward, or away from the ball. Unless the ball happened to hit the racket precisely at the racket's center of mass, the racket would additionally experience a rotational motion around its center of mass—much as a penny that has been struck near its edge will start to spin. Whenever the ball hits the racket face, the effect of this rotational motion will be to jerk the end of the handle forward, towards the ball. Depending on where the ball strikes the racket face, one or the other of these motions will predominate.

However, there is one point of impact, known as the center of percussion, which causes neither motion to predominate; if a ball were to strike this point, the impact would not impart any motion to the end of the handle. The reason for this lack of motion is that the force on the upper part of the hand would be equal and opposite to the force on the lower part of the hand, resulting in no net force on the tennis players’ hand or forearm. The center of percussion constitutes a second sweet spot because a tennis player's wrist typically is placed next to the end of the racket's handle. When the player strikes the ball at the center of percussion, her wrist is jerked neither forward nor backward, and she experiences a relatively smooth, comfortable tennis stroke.

The manner in which a tennis player can detect the center of percussion on a given tennis racket follows from the nature of this second sweet spot. The center of percussion can be located via simple trial and error by holding the end of a tennis racket between your finger and thumb and throwing a ball onto the strings. If the handle jumps out of your hand, then the ball has missed the center of percussion.
What is the primary message the author is trying to convey?

(A) A proposal for an improvement to the design of tennis rackets
(B) An examination of the differences between the two types of sweet spot
(C) A definition of the translational and rotational forces acting on a tennis racket
(D) A description of the ideal area in which to strike every ball
(E) An explanation of a lesser-known area on a tennis racket that dampens unwanted vibration

[Reveal] Spoiler: OA
E

According to the passage, all of the following are true of the forces acting upon a tennis racket striking a ball EXCEPT

(A) the only way to eliminate the jolt that accompanies most strokes is to hit the ball on the center of percussion
(B) the impact of the ball striking the racket can strain a tennis player's arm
(C) there are at least two different forces acting upon the racket
(D) the end of the handle of the racket will jerk forward after striking the ball unless the ball strikes the racket's center of mass
(E) the racket will rebound after it strikes the ball

[Reveal] Spoiler: OA
A

What is the primary function served by paragraph two in the context of the entire passage?

(A) To establish the main idea of the passage
(B) To provide an explanation of the mechanics of the phenomenon discussed in the passage
(C) To introduce a counterargument that elucidates the main idea of the passage
(D) To provide an example of the primary subject described in the passage
(E) To explain why the main idea of the passage would be useful for tennis players

[Reveal] Spoiler: OA
B

The author mentions “a penny that has been struck near its edge” in order to

(A) show how the center of mass causes the racket to spin
(B) argue that a penny spins in the exact way that a tennis racket spins
(C) explain how translational motion works
(D) provide an illustration of a concept
(E) demonstrate that pennies and tennis rackets do not spin in the same way

[Reveal] Spoiler: OA
D

Which of the following can be inferred from the passage?

(A) If a player holds the tennis racket anywhere other than the end of the handle, the player will experience a jolting sensation.
(B) The primary sweet spot is more effective at damping vibration than is the secondary sweet spot.
(C) Striking a tennis ball at a spot other than the center of percussion can result in a jarring feeling.
(D) Striking a tennis ball repeatedly at spots other than a sweet spot leads to “tennis elbow.”
(E) If a player lets go of the racket at the moment of impact, the simultaneous forward and backward impetus causes the racket to drop straight to the ground.

[Reveal] Spoiler: OA
C

Select the sentence in the second or third paragraph that describes the physics of the center of percussion's perceived “sweetness.”

[Reveal] Spoiler: OA
The reason for this lack of motion is that the force on the upper part of the hand would be equal and opposite to the force on the lower part of the hand, resulting in no net force on the tennis players’ hand or forearm

It can be inferred that a tennis ball that strikes a racket's center of percussion will do which of the following?

Indicate $$all$$ that apply.

Cause the racket to bounce backwards
Not cause the wrist to jerk
Allow for a cleaner stroke than a ball striking a racket's primary sweet spot

[Reveal] Spoiler: OA
B,C

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Re: Though most tennis players generally strive to strike the ba [#permalink]  09 Nov 2018, 11:16
I have a question about the last question.

I picked B only. (Not cause the wrist to jerk)

I did not pick C. (Allow for a cleaner stroke than a ball striking a racket's primary sweet spot)

This is because I didn't see sentence that says that hitting the center of percussion gives a cleaner stroke than the vibration node.

The only sentence on this that I saw was: When the player strikes the ball at the center of percussion, her wrist is jerked neither forward nor backward, and she experiences a relatively smooth, comfortable tennis stroke.

So there is no comparison. The word "relatively" is not specifically used to compare it to the vibration node. Relatively here is used more to mean "more than in usual circumstances."

Did I miss something?
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Re: Though most tennis players generally strive to strike the ba [#permalink]  10 Nov 2018, 17:43
Could the reason why the answer to the final question includes C "Allow for a cleaner stroke than a ball striking a racket's primary sweet spot?

The passage didn't mention that one was better than the other. It just mentioned that the second sweet spot was less known.
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Re: Though most tennis players generally strive to strike the ba [#permalink]  11 Nov 2018, 10:48
Expert's post
Quote:
The center of percussion constitutes a second sweet spot because a tennis player's wrist typically is placed next to the end of the racket's handle. When the player strikes the ball at the center of percussion, her wrist is jerked neither forward nor backward, and she experiences a relatively smooth, comfortable tennis stroke.

From this, you could certainly infer that C is correct. However, the passage nowhere is mentioned a comparison between a ball that hits the primary and secondary sweet spot.

In this is a bit confusing the formulation of C. Notwithstanding, C is correct.

Regards
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Re: Though most tennis players generally strive to strike the ba [#permalink]  12 Nov 2018, 12:32
Carcass wrote:
Quote:
The center of percussion constitutes a second sweet spot because a tennis player's wrist typically is placed next to the end of the racket's handle. When the player strikes the ball at the center of percussion, her wrist is jerked neither forward nor backward, and she experiences a relatively smooth, comfortable tennis stroke.

From this, you could certainly infer that C is correct. However, the passage nowhere is mentioned a comparison between a ball that hits the primary and secondary sweet spot.

In this is a bit confusing the formulation of C. Notwithstanding, C is correct.

Regards

Thank you for your feedback. I'm still confused by C but you win some and let others go.
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Re: Though most tennis players generally strive to strike the ba [#permalink]  12 Nov 2018, 23:03
Expert's post
The problem here is actually this

Quote:
Allow for a cleaner stroke than a ball striking a racket's primary sweet spot

From the red part, you certainly might infer that C is correct.

However, from the bold part NO. Where is the comparison ??

In this tiny details, the difference between the OG material and a good NON official material is all about.

Regards
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Re: Though most tennis players generally strive to strike the ba [#permalink]  13 Nov 2018, 17:42
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KUDOS
Carcass wrote:
The problem here is actually this

Quote:
Allow for a cleaner stroke than a ball striking a racket's primary sweet spot

From the red part, you certainly might infer that C is correct.

However, from the bold part NO. Where is the comparison ??

In this tiny details, the difference between the OG material and a good NON official material is all about.

Regards

You are excellent in teaching!
If only I was aware of this site before.
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Re: Though most tennis players generally strive to strike the ba [#permalink]  12 Aug 2019, 05:24
I have question with the fifth question.
The answer choice of this is C--(C) Striking a tennis ball at a spot other than the center of percussion can result in a jarring feeling.
Then how about the sweet spot referred in the first paragraph?
thanks
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Re: Though most tennis players generally strive to strike the ba [#permalink]  13 Aug 2019, 15:03
Expert's post
Not quite sure to get what you do mean.

However, c is correct because if the ball hits exactly the center or percussion the result is neutral.

Other than this point, the racket always transmits one effect or another to the wrist and forearm of the player.

Regards
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Re: Though most tennis players generally strive to strike the ba   [#permalink] 13 Aug 2019, 15:03
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