# What Is The Maximum Force The Locust Exerted on The Plate?

BurpHa
Homework Statement:
The jumping ability of the African desert locust was measured by placing the insect on a force plate, a platform that can
accurately measure the force that acts on it. When the locust
jumped straight up, its acceleration was measured to follow the
curve in Figure P4.71. What was the maximum force that this
0.50 g locust exerted on the force plate?
Relevant Equations:
Newton's Second Law: F = ma.
At the beginning, I just looked for the highest point in the graph, which is approximately 90 \frac m s^2.
Then I plugged it in the formula F = ma and got the force equaled to 0.045 N.

However, when I looked back, the graph is about the change in acceleration. So really, I'm dealing with acceleration of acceleration. From what I understand, the acceleration increases when the locust jumps up until t is approximately about 27 ms, when it starts to decrease.

The answer I get from my book is 0.084 N. When I plug 0.084 N to the formula F = ma, the acceleration is 168 \frac m s^2

I don't understand how it got 168 \frac m s^2 so that it could get 0.084 N.

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The rate of change of acceleration is called jerk. But, that's not relevant here.

I'm not sure how the book got its answer, but you did forget something!

BurpHa
The rate of change of acceleration is called jerk. But, that's not relevant here.

I'm not sure how the book got its answer, but you did forget something!
Do you mean the gravitational force?

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Do you mean the gravitational force?
Yes.

BurpHa
Do you mean the gravitational force?
Yes, I've been trying to understand how the book (College Physics: A Strategic Approach 4th edition by knight, jones, and field) got its answer

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Yes, I've been trying to understand how the book (College Physics: A Strategic Approach 4th edition by knight, jones, and field) got its answer
I can't help you there. I just googled for "speed of jumping locust" to corroborate their data. You couldn't do that when I was a student!

BurpHa
I can't help you there. I just googled for "speed of jumping locust" to corroborate their data. You couldn't do that when I was a student!
I also googled, but the answer I got was the one I got, 0.045 N.

• PeroK
BurpHa
I can't help you there. I just googled for "speed of jumping locust" to corroborate their data. You couldn't do that when I was a student!
But the thing is that the acceleration changes when the locust in in its motion. According to the graph, it looks like the acceleration increases when the locust jumps up.

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I also googled, but the answer I got was the one I got, 0.045 N.
For such a high acceleration, the extra force to overcome gravity is not as significant as it would normally be.

BurpHa
For such a high acceleration, the extra force to overcome gravity is not as significant as it would normally be.
So you agree the answer is 0.045 N? I mean, we don't have a fixed acceleration as we do in other problems. This time, the acceleration changes as the locust progresses through its jump.

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So you agree the answer is 0.045 N?

BurpHa
Do you think 0.084 N is the correct answer?

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Do you think 0.084 N is the correct answer?
Does adding 10% to 0.045 give 0.084?

• PeroK
BurpHa
Does adding 10% to 0.045 give 0.084?
No. But my book gave 0.084 N as the answer. I did get your result when I tried the problem.

BurpHa
Does adding 10% to 0.045 give 0.084?
There is a period when the acceleration increases, and that is what I don't understand. I mean, when you apply a force, the acceleration should be constant.

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There is a period when the acceleration increases, and that is what I don't understand. I mean, when you apply a force, the acceleration should be constant.
only if the force is constant.

• PeroK
BurpHa
only if the force is constant.
So you take a = 90 m / s ^ 2. But for the most part, the acceleration increases, so why you choose this acceleration? I did what you did until I realized the acceleration is not constant.

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There is a period when the acceleration increases, and that is what I don't understand. I mean, when you apply a force, the acceleration should be constant.
The acceleration (increasing velocity) of any constant mass is a consequence of the magnitude of the net force that is applied to it.

In this case, the net force increases as time goes by, reaches a peak, and decreases again.
The reason is the mechanism of the legs and muscles of the insect, which provide a different amount of force as they extend.

On the other hand, the weight (force induced by gravity) of the insect remains constant during the process.

The net force mentioned above is the vectorial summation of leg's force and weight.

http://hyperphysics.phy-astr.gsu.edu/hbase/avari.html

• BurpHa
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So you take a = 90 m / s ^ 2. But for the most part, the acceleration increases, so why you choose this acceleration?
Because it asks for the maximum force.

• BurpHa
BurpHa
The acceleration (increasing velocity) of any constant mass is a consequence of the magnitude of the net force that is applied to it.

In this case, the net force increases as time goes by, reaches a peak, and decreases again.
The reason is the mechanism of the legs and muscles of the insect, which provide a different amount of force as they extend.

On the other hand, the weight (force induced by gravity) of the insect remains constant during the process.

The net force mentioned above is the vectorial summation of leg's force and weight.

http://hyperphysics.phy-astr.gsu.edu/hbase/avari.html
Thanks, a bit of biology helps.

• Lnewqban
BurpHa
Because it asks for the maximum force.
I agree, but I don't know why my textbook gives the result as 0.084 N.

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I agree, but I don't know why my textbook gives the result as 0.084 N.
It could be a typo or it could be that the person who who provided the solution made a mistake. Wrong solution answers appear once in a while. I agree with your answer.

• erobz and BurpHa
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I searched for the question online. Got several hits, all the same graph, just small variations in locust mass.
All were on paywalled student help sites, though you could sign up for a free trial. The only one I looked further into was Brainly. The "expert verified" solution it showed quoted "Fnet=ma-mg". At that point I gave up.

• BurpHa
BurpHa
I searched for the question online. Got several hits, all the same graph, just small variations in locust mass.
All were on paywalled student help sites, though you could sign up for a free trial. The only one I looked further into was Brainly. The "expert verified" solution it showed quoted "Fnet=ma-mg". At that point I gave up.
Brainly is not reliable, those "expert verified" thing is rubbish. Yeah, most of the other sites are paid, that is why I look at my textbook's solution to check ;))) By the way, thank you for your help!!

• Lnewqban
BurpHa
Homework Statement:: The jumping ability of the African desert locust was measured by placing the insect on a force plate, a platform that can
accurately measure the force that acts on it. When the locust
jumped straight up, its acceleration was measured to follow the
curve in Figure P4.71. What was the maximum force that this
0.50 g locust exerted on the force plate?
Relevant Equations:: Newton's Second Law: F = ma.

At the beginning, I just looked for the highest point in the graph, which is approximately 90 \frac m s^2.
Then I plugged it in the formula F = ma and got the force equaled to 0.045 N.

However, when I looked back, the graph is about the change in acceleration. So really, I'm dealing with acceleration of acceleration. From what I understand, the acceleration increases when the locust jumps up until t is approximately about 27 ms, when it starts to decrease.

The answer I get from my book is 0.084 N. When I plug 0.084 N to the formula F = ma, the acceleration is 168 \frac m s^2

I don't understand how it got 168 \frac m s^2 so that it could get 0.084 N.

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