A child pulls a sled with a mass of m = 4 kg, with a force F which makes an angle ά in the direction of movement and prints an acceleration of 3 m / s2. If the friction force between the sled and snow is Ff = 5N, what is the mechanical work value performed by the child to the sled on the distance of 4 m?

A child pulls a sled with a mass of m = 4 kg, with a force F which makes an angle ά in the direction of movement and prints an acceleration of 3 m / s2.

If the friction force between the sled and snow is Ff = 5N, what is the mechanical work value performed by the child to the sled on the distance of 4 m?

Solution:

The force that produces mechanical work is:

Force : Fx = Fcos ά 

we calculate the force that produce mechanical work by applying the fundamental relation of dynamics when the sled moves:

Ff  + N + F + mg = ma       (relation 1)

Using relation 1 on the direction of Ox axis we obtain:

-Ff + Fcos ά = ma

=> Fcos ά = ma +Ff

The mechanical work produced by the force F is given by relation:

L = (Ff + ma)*d

=> (5N + 4 Kg + 3m/s²) * 4

=> L = 68 jouli

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