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Newton's Second Law and Acceleration

Newton's Second Law: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

Newton's Second Law of Motion means that if you push twice as hard, then you get twice the acceleration. If your push three times as hard, then you get three times the acceleration and so on. (directly proportional) If you have the same force and an object with twice the mass you will have half the acceleration. Just like if you had three times the mass you would have one third the acceleration.

Fnet = ma

m stands for the mass (kg) of the object and a stands for the acceleration (m/s/s). Where Fnet is the net force that is acting on the object (N, newtons).


An object has a mass of 20.41 kg and an acceleration of 8.22 m/s2. What is the force on the object?

Answer: You have the mass and the acceleration of the object so you can easily figure out the force. All you have to do is apply Newton's Second Law of Motion.

Fnet = ma

= (20.41 kg)(8.22 m/s2)

= 167.8 N


An electron has a mass of 9.11 x 10-31. It is moved a distance of 6.0 mm and accelerated by a net electrical force of 4.6 x 10 -10 N. If it started from rest, find it’s acceleration and final velocity.

Answer: A.) To find the acceleration use Newton's Second Law of Motion

Fnet= ma

4.6 x 10 -10 N = (9.11 x 10-31)(a)

a = 5.0 x 1020 m/s2

B.) To find the final velocity use the formula Vf2 = Vi2 + 2ad. Remember to convert the units, (distance must be in meters).

Vf2 = Vi2 + 2ad

Vf2 = 02 + 2(5.0 x 1020)(0.006)

Vf2 = 6.0 x 1018 m/s

Vf = 2.5 x 109 m/s

more Newton's Second Law problems

Newton's Second Law problems involving friction or weight

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Shanleigh Sutherland

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