A block of mass M rests on a block of mass M1 = 5.00 kg which is on a tabletop. A light string passes over a frictionless peg and connects the blocks. The coefficient of kinetic friction μk at both surfaces equals 0.330. A force of F = 56.0 N pulls the upper block to the left and the lower block to the right. The blocks are moving at a constant speed.

Required:
Determine the mass of the upper block.

Respuesta :

Answer:

The mass of the upper block M = 4.12 kg

Explanation:

From the given information:

The upper block formula can be computed as :

[tex]F = T + F_{f1}[/tex]

[tex]F - T - F_{f1} =0[/tex]

where;

[tex]F_{f1} = \mu Mg[/tex]

[tex]F - T - \mu Mg=0 ---- (1)[/tex]

The lower block formula is as follows:

[tex]T - F_{f1} -F_{f2} = 0[/tex]

[tex]T - \mu Mg - \mu (M_1+M)g= 0[/tex]

[tex]T = \mu Mg - \mu (M_1+M)g --- (2)[/tex]

Equating equation (1) and  (2) together, we have:

[tex]F - \mu Mg - \mu Mg - \mu (M_1 + M) g = 0[/tex]

[tex]56 - 3 Mg - \mu M_1g= 0[/tex]

[tex]M = \dfrac{56 - \mu M_1 g}{3 \mu g}[/tex]

[tex]M = \dfrac{56 - (0.330)(5)(9.8)}{3 (0.330) (9.8)}[/tex]

[tex]M = \dfrac{56 - 16.17}{9.702}[/tex]

[tex]M = \dfrac{39.83}{9.702}[/tex]

M = 4.12 kg

Block on a horizontal surface

We are given;

Coefficient of kinetic friction for both surfaces; μ_k = 0.33

Force; F = 56 N

Mass of lower block; m1 = 5 kg

From the image of this block and string system, we can find the sum of forces to get;

F = T + F_f1

Where;

T is tension in string

F_f1 is frictional force = μ_k × mg

Thus;

F = T + μ_k*mg - - - (1)

Where m is mass of the upper block

For the lower block, we can sum forces to get;

T = μ_k*mg + μ_k(m1 + m)g - - - (2)

Put μ_k*mg + μ_k(m1 + m)g for T in eq 1;

F = μ_k*mg + μ_k(m1 + m)g + μ_k*mg

F = 2μ_k*mg + μ_k(m1 + m)g

56 = (μ_k*g) * (2m + m1 + m)

56 = (0.33 * 9.8) * (3m + 5)

3m + 5 = 56/(0.33 * 9.8)

3m + 5 = 17.316

m = (17.316 - 5)/3

m = 4.11 kg

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