Diving Board Torque with No Mass Given For the Diver

[jweica]

The board is 4m and has 2 supports: support 1 exerts 5400N and support 2 exerts 6000N before the diver performs the dive.
Neglecting the mass of the board, what is the force on the board due to the weight of the diver?

My attempt at this question: FS2 - FS1 = 6000 - 5400 = 600N
But I'm having difficulty on solving this question due to not really understanding on what to do with the given information...

Thanks!

 

[PhanthomJay]

Well u have the right answer, but was it a good guess? You should tell us which support has the 6000 N force, and which has the 5400 N force, and in which direction do they act on the board. In which direction does the normal force from the persons weight act on the board ? Please explain your reasoning and what equations are you using. Thanks.

 

[jweica]

Well u have the right answer, but was it a good guess? You should tell us which support has the 6000 N force, and which has the 5400 N force, and in which direction do they act on the board. In which direction does the normal force from the persons weight act on the board ? Please explain your reasoning and what equations are you using. Thanks.

Hello! I have attached a screenshot of my poor illustrated free body diagram. From the FBD, support 1 is acting downwards so it would be -5400N, and support 2 is acting upwards, therefore, in the positive direction... so 6000N.
Overall, the person's weight (I'm assuming) wouldn't put out as much force by just standing there before the dive... so the force should be less than the force at the supports. So the person's force ends up acting upwards

Thank you replying!

 

[PhanthomJay]

Hello! I have attached a screenshot of my poor illustrated free body diagram. From the FBD, support 1 is acting downwards so it would be -5400N, and support 2 is acting upwards, therefore, in the positive direction... so 6000N.
Overall, the person's weight (I'm assuming) wouldn't put out as much force by just standing there before the dive... so the force should be less than the force at the supports. So the person's force ends up acting upwards
s breve
ate Thank you replying!

Ok with forces and direction at supports. Correct.
So if you have 5400 N down and 6000 N up , the weight of the person by Newton’s first law is 600 N, in what direction? Hint: a persons weight is the force of gravity acting on him or her. In what direction does gravity act??

Oh you are a newbie here, I forgot to welcome you to PF!

 

[jweica]

Ok with forces and direction at supports. Correct.
So if you have 5400 N down and 6000 N up , the weight of the person by Newton’s first law is 600 N, in what direction? Hint: a persons weight is the force of gravity acting on him or her. In what direction does gravity act??

Oh you are a newbie here, I forgot to welcome you to PF!

The problem has parts to it, and I'm supposed to find the diver's weight in the second part of this problem
I figured that gravity is a downwards force, but the weight was the diver is unknown. Since the first part of the problem asked to find the force of board due weight of the diver (assuming that the diver is standing still on the board), I figured that I should just simply use: Fnet = FS2 - FS1 = 600N

While solving for the weight of the diver, all of the forces are downwards. So I just did: FYnet = FS1 + FS2 + Diver = -5400 + 6000 + (mDiver)(-9.81) = (600/9.81) = 61.16kg

Haha thank you for the welcome! :)

 

[PhanthomJay]

The problem has parts to it, and I'm supposed to find the diver's weight in the second part of this problem
I figured that gravity is a downwards force, but the weight was the diver is unknown. Since the first part of the problem asked to find the force of board due weight of the diver (assuming that the diver is standing still on the board), I figured that I should just simply use: Fnet = FS2 - FS1 = 600N

While solving for the weight of the diver, all of the forces are downwards. So I just did: FYnet = FS1 + FS2 + Diver = -5400 + 6000 + (mDiver)(-9.81) = (600/9.81) = 61.16kg

Haha thank you for the welcome! :)

In the SI system of measure, the unit of force, and hence weight, is the Newton. There is no need to calculate the diver’s mass in kg. It is common perhaps in the Lay community to express mass units instead of force units, you know, like buying a kg of bananas and not 9.8 N of bananas. But in physics, you must keep units consistent.
Now not all forces are downward. Assume upward forces are positive and downward forces are negative. From Newton 1, the sum of all forces acting on the board must be 0 since the system is st rest. Thus:
FS1 + FS2 + Diver weight = 0. Rearranging,
Diver Weight = -FS1 - FS2
Diver Weight = - (-5400) - 6000
Diver Weight = 5400 -6000
Diver Weight = -600 N

The negative -600 means that the weight acts down, since we chose the down direction to be negative. You have the right answer, both in force and mass units, but I just want to be sure you are ok with signs and their meaning here, because they can get very confusing for sure.

 

[jweica]

In the SI system of measure, the unit of force, and hence weight, is the Newton. There is no need to calculate the diver’s mass in kg. It is common perhaps in the Lay community to express mass units instead of force units, you know, like buying a kg of bananas and not 9.8 N of bananas. But in physics, you must keep units consistent.
Now not all forces are downward. Assume upward forces are positive and downward forces are negative. From Newton 1, the sum of all forces acting on the board must be 0 since the system is st rest. Thus:
FS1 + FS2 + Diver weight = 0. Rearranging,
Diver Weight = -FS1 - FS2
Diver Weight = - (-5400) - 6000
Diver Weight = 5400 -6000
Diver Weight = -600 N

The negative -600 means that the weight acts down, since we chose the down direction to be negative. You have the right answer, both in force and mass units, but I just want to be sure you are ok with signs and their meaning here, because they can get very confusing for sure.

Ohhhhh okay that makes more sense! Thank you so much for clarifying this for me!