Why Do My Physics Calculations Keep Giving Incorrect Results?

  • Thread starter Lorelyn
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In summary: Remember to always check your units and make sure they are consistent throughout your calculations. In summary, the first problem involved finding the force of the air on a helicopter lifting a truck, while the second problem involved finding the force that stops a car when the brakes are applied. The correct solutions are 52000N and 4319.45N respectively.
  • #1
Lorelyn
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Homework Statement



A 21000 kg helicopter is lifting a 5000 kg truck with an upward acceleration of 2.00 m/s2. Calculate the force the air exerts on the helicopter blades.

Homework Equations



F=ma

The Attempt at a Solution



I did the total force is equal to the sum of the two masses(26000kg) times the acceleration (2) which gave me 52000N. Which is apparently wrong but I have no idea why...

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Homework Statement




A car that weighs 14200.0 N is initially moving at a speed of 44.0 km/hr ((or 12.222)m/s) when the brakes are applied and the car is brought to a stop in 4.1 s. Find the magnitude of the force that stops the car, assuming it is constant.

Homework Equations



F=ma, Vf = Vi+ at

The Attempt at a Solution



So I solve using kinematics to get the acceleration (-12.22=(a*4.1)) so a = 2.98m/s^2. Which I then multiply by 14200/9.8 (the mass) to get the force equaling 4319.45N. Which is, again, wrong. And as with the above question I don't know why. I've done everything right as far as i can tell...
 
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  • #2
helicopter

Lorelyn said:

Homework Statement



A 21000 kg helicopter is lifting a 5000 kg truck with an upward acceleration of 2.00 m/s2. Calculate the force the air exerts on the helicopter blades.

Homework Equations



F=ma

The Attempt at a Solution



I did the total force is equal to the sum of the two masses(26000kg) times the acceleration (2) which gave me 52000N. Which is apparently wrong but I have no idea why...
You found the net force, but the question asks for the force of the air. What other force acts on this system?
 
  • #3
car

Lorelyn said:

Homework Statement




A car that weighs 14200.0 N is initially moving at a speed of 44.0 km/hr ((or 12.222)m/s) when the brakes are applied and the car is brought to a stop in 4.1 s. Find the magnitude of the force that stops the car, assuming it is constant.

Homework Equations



F=ma, Vf = Vi+ at

The Attempt at a Solution



So I solve using kinematics to get the acceleration (-12.22=(a*4.1)) so a = 2.98m/s^2. Which I then multiply by 14200/9.8 (the mass) to get the force equaling 4319.45N. Which is, again, wrong. And as with the above question I don't know why. I've done everything right as far as i can tell...
This one looks fine to me.
 

Related to Why Do My Physics Calculations Keep Giving Incorrect Results?

What is the concept of "Forces - Solved, but wrong?"

The concept of "Forces - Solved, but wrong" refers to when a problem or equation involving forces is solved, but the solution is incorrect due to a mistake made in the process of solving it.

Why is it important to double check solutions for forces?

It is important to double check solutions for forces because a small error in the calculation or understanding of the problem can lead to a drastically incorrect solution, which can have serious consequences in real-world applications.

What are some common mistakes made when solving forces?

Some common mistakes made when solving forces include using the wrong direction for a force, forgetting to account for all forces acting on the object, and incorrectly applying mathematical formulas.

How can one avoid making mistakes when solving forces?

To avoid making mistakes when solving forces, it is important to carefully read and understand the problem, draw accurate diagrams, use the correct units, and double check all calculations and assumptions made.

What should one do if they realize they have made a mistake in solving forces?

If one realizes they have made a mistake in solving forces, they should retrace their steps and correct the error. It is also helpful to have someone else review the solution to catch any mistakes that may have been missed.

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