A boy is pulling a 150 kg crate with a force of 1150 N. If the crate experiences a frictional force of 490 N, find: a) The acceleration of the crate.

b) The normal force acting on the crate.

First, let's find the resultant, and applicate 2nd law of Newton using the resultant, so:

R = ma

F - Ff = ma

Data:

F = Force = 1150 N

Ff = Friction force = 490 N

m = Mass = 150 kg

a = Aceleraction = ?

Replacing according our data:

1150 N - 490 N = 150 kg * a

660 N = 150 kg * a

660 N / 150 kg = a

a = 4,4 m/s²   ← Aceleration of the object

The normal force IS NOT the resultant force, the normal force's the force between the ground and the object, in another words, is the weight of the object, and for the weight:

w = mg

w = 150 kg * 10 m/s²

w = 1500 N   ← Normal force between object and ground.

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