Calculating Mass of Little Sister Using Newton's Second Law

AI Thread Summary
To calculate the mass of the little sister being pulled on a sled, the equation F = (m1 + m2) * a is used, where F is the force, m1 is the mass of the sled, and a is the acceleration. Given a force of 110 N, an acceleration of 2.5 m/s², and a sled mass of 7 kg, the equation simplifies to m2 = (F/a) - m1. This results in the correct mass of the little sister being 37 kg. The initial miscalculation arose from incorrect application of the formula, but the correct steps yield the desired result. Understanding the relationship between force, mass, and acceleration is key to solving such problems.
Propaganda777
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You are pulling your little sister on her sled acroos an icy(frictionless) surface. When you exert a constant horizontal force of 110 N, the sled has an acceleration of 2.5 m/s^2. If the sled has a mass of 7 kg, what is the mass of your little sister?

Heres how I attempted it:
F=110N
A=2.5 m/s^2
M1= 7kg
M2= ?

F=(M1+M2) A
M2= 41.2 kg


The answer is 37 kg, but I can't figure out how to arrive at this mass. Can anyone help me?
 
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Propaganda777 said:
F=(M1+M2) A
Since you know F and A, you can solve for M1 + M2. Then just subtract out M1.
 
I did, but it comes out to a wrong answer:

F= (m1+m2)a

m2=(F-m1)/a

m2=41.2kg

The answer should be 37 kg, right?
 
Propaganda777 said:
I did, but it comes out to a wrong answer:

F= (m1+m2)a

m2=(F-m1)/a
That last step doesn't follow. Do this:
F = (m1 + m2)a
F/a = m1 + m2

What's that equal?
 
hey it works, thanks you:)
 
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