A 2.00 kg aluminum block and a 6.20 kg copper block are connected by a light str

Question

A 2.00 kg aluminum block and a 6.20 kg copper block are connected by a light string over a frictionless pulley. They sit on a steel surface, as shown in Figure P5.38, where = 30.0°.

When they are released from rest, will they start to move? Refer to Table 5.1 for the coefficients of friction.

1 Correct answer is No for this part

What is...

Determine the sum of the magnitudes of the forces of friction acting on the blocks.
??? N

Explanation / Answer

Applying Newton’ second law to m1,

T-km1g=m1a   ………………….Here k=coefficient of static friction between Aluminum and mild steel=0.47

T= km1g+m1a----------------(1)

Applying Newton’ second law to m2,

m2gsinq-T- km2gcosq-=m2a ------------------(2) ………………….Here k=coefficient of static friction between Aluminum and mild steel=0.36

Plugging (1) in (2)

m2gsinq- km1g-m1a- km2gcosq =m2a

a= (m2gsinq- km1g- km2gcosq)/(m1+m2)

a = (6.2*9.8*sin30-0.47*2*9.8-0.36*6.2*cos30)/(2+6.2) = 0.51 m/s2 = 2.35m/s2

Plugging this value in (1)

T= km1g+m1a= (0.47*2*9.8+2*2.35) = 13.9 N

Sum of magnitudes of forces of friction = (km1g+ km2gcosq) = (0.47*2*9.8+0.36*6.2*cos30) = 11.14 N

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