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# ch5 - 5.8 IDENTIFY Apply Newton's 1st law to the wrecking...

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5.8. I DENTIFY : Apply Newton’s 1st law to the wrecking ball. Each cable exerts a force on the ball, directed along the cable. S ET U P : The force diagram for the wrecking ball is sketched in Figure 5.8. Figure 5.8 E XECUTE : (a) y y F ma = cos40 0 B T mg ° − = 2 4 (4090 kg)(9.80 m/s ) 5.23 10 N cos40 cos40 B mg T = = = × ° ° (b) x x F ma = sin40 0 B A T T ° − = 4 sin40 3.36 10 N A B T T = ° = × E VALUATE : If the angle 40 is replaces by (cable B is vertical), then and ° 0 ° B T mg = 0. A T = 5.14.I DENTIFY : Apply m = F a G G to each block. 0 a = . S ET U P : Take perpendicular to the incline and y + x + parallel to the incline. E XECUTE : The free-body diagrams for each block, A and B , are given in Figure 5.14. (a) For B , x x F ma = gives 1 sin 0 T w α = and 1 sin T w α = . (b) For block A , x x F ma = gives 1 2 sin 0 T T w α = and 2 2 sin T w α = . (c) y y F ma = for each block gives cos A B n n w α = = . (d) For 0 α , and . For , 1 2 0 T T = A B n n w = 90 α ° 1 T w = , and . 2 2 T = w 0 A B n n = = E VALUATE : The two tensions are different but the two normal forces are the same. Figure 5.14a, b 5.21.I DENTIFY : Apply m F = a G G to each block. Each block has the same magnitude of acceleration a .

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