# Average resistance = -5395.5/0.075Average resistance=-71940N

• Grinter1
In summary, The conversation is about a physics problem where a pile-driver hammer of mass 150kg falls freely a distance of 5m to strike a pile of mass 400kg and drives it 75mm in the ground without rebound. The problem requires the use of the principle of conservation of momentum and D'lamberts principle to calculate the average resistance of the ground. The attempt at a solution provided by the person asking the question is hard to decipher due to incorrect definition of variables and lack of units. A suggestion was given to start over with proper definitions and including units in the solution to avoid errors.
Grinter1
Could you tell me if i am right please and if I am wrong could you point out any mistakes?

A pile-driver hammer of mass 150kg falls freely a distance of 5m to strike a pile of mass 400kg and drives it 75mm in the ground. The hammer doesn't rebound when driving the pile. Calculate the average resistance of the ground. You are required to solve this problem by:
(a)By making use of the principle of conservation of momentum and D'lamberts principle

2. Homework Equations
v=u+at
v2(squared)=u2(squared)+2as
S=ut+0.5at2(squared)
f=m*a

3. The Attempt at a Solution

a)
Hammer mass=150kg
Falls freely= gravity = 9.81
Distance= 5m
pile mass =400kg
depth= 75mm= 0.075m
no rebound
Average resistance= ?

M1*U1+M2*U1=M3*V1
(150*9.81)+(400*0)=1471.5 m/s

a=v(squared)-U(squared)/2*5
a= 0.981
f=m*a
f=147.15

FR=f-m*a-m*g
FR= -5395.5

Grinter1 said:
a)
Hammer mass=150kg
Falls freely= gravity = 9.81
Distance= 5m
pile mass =400kg
depth= 75mm= 0.075m
no rebound
Average resistance= ?

M1*U1+M2*U1=M3*V1
(150*9.81)+(400*0)=1471.5 m/s

That French guy have been called D'Alembert.

Your solution is hard to decipher, because you did not define your variables correctly, and it seems
you are switching them in the middle of the solution.
It seems you meant
M1 = 150 kg //hammer mass
U1 = 9.81 m/s^2 //gravitational acceleration on Earth surface
M2 = 400 kg //mass of pile
U2 = 0 m/s^2 //acceleration of pile (I guess you meant U2 at the second instance of U1)

so
M1*U1+M2*U2=150 kg * 9.81 m/s^2 + 400 kg * 0 m/s^2 = 1471.5 kg*m/s^2
notice the difference in units between your and my solution!

This far I could go with deciphering your solution. Maybe this could be the cause that you get an answer so hardly.

I would suggest to start over, define your variables, and always write units.
Defining your variables helps you to understand yourself (and others to understand you, but it is secondary)
Imagine when you are in the middle of a lengthy solution. You cannot afford to mix two variables because
they are not defined clearly. And in the beginning even this problem can be lengthy for you.
Writing units helps you to spot errors (And cheating in the exam by coming up with forgotten equations correctly based only on the units of variables involved. Serious scientists also do this, and call it dimensional analysis.).

## 1. What does "Average resistance = -5395.5/0.075Average resistance=-71940N" mean?

This equation represents the average resistance, measured in newtons (N), in a given system. The value of -5395.5/0.075 represents the ratio of the total resistance in the system to the applied force. The resulting average resistance is -71940N.

## 2. How is average resistance calculated?

Average resistance is calculated by dividing the total resistance in a system by the applied force. This can be represented by the equation: Average resistance = Total resistance / Applied force.

## 3. What units are used to measure average resistance?

Average resistance is typically measured in units of ohms (Ω) or newtons (N). The specific unit used may depend on the type of resistance being measured and the context of the system.

## 4. How is average resistance related to electrical circuits?

In electrical circuits, average resistance refers to the overall opposition to current flow in the circuit. It is calculated by dividing the total voltage in the circuit by the total current. This relationship is represented by the equation: Average resistance = Total voltage / Total current.

## 5. Can average resistance be negative?

Yes, average resistance can be negative. This occurs when the applied force is greater than the total resistance in the system, resulting in a negative ratio and average resistance value. Negative resistance is often seen in complex circuits or systems with non-linear components.

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