A 2.00 kg aluminum block and a 6.20 kg copper block are connected by a light str
ID: 1357486 • Letter: A
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. Yes or No ??
If so, determine the following. Enter a zero in each box if they do not move.
If not, determine the sum of the magnitudes of the forces of friction acting on the blocks. Enter zero if they do in fact move.
???
Explanation / Answer
1 . YES
a)
coefficients of friction values on
Aluminum on steel 0.47 = µalluminium
Copper on steel 0.36 = µcopper
a = g( m2(sin - µcopper cos ) - µalluminium m1) /( m1 + m2 )
a = 9.8 ( 6.2 ( sin30 - 0.36 cos30 ) - 0.47 X 2) / 8.2
a = 9.8 ( ( 6.2 X (0.5 - 0.36 X 0.86) - 0.94) / 8.2
a = 9.8 ( ( 6.2 X (0.5 - 0.3096) - 0.94) / 8.2
a = 9.8 ( 6.2 X (0.19) - 0.94 ) / 8.2
a = 9.8(1.178 - 0.94 ) / 8.2
a = 9.8 (0.238)/8.2
a = 2.33 / 8.2
a = 0.284 m/s2
b)
T = 2 X 0.284 + 0.47 X 2 X 9.8
T = 0.568 + 9.212
T = 9.78 N
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