FIGURE 6-11
-Refer to Figure 6-11. Block A has a mass of 3.00 kg and rests on a smooth table and is connected to block B, which has a mass of 2.00 kg, after passing over an ideal pulley, as shown. Block B is released from rest. How long does it take block B to travel 80.0 cm?
A) 0.404 s
B) 0.494 s
C) 0.639 s
D) 0.785 s
E) 0.935 s

Question

FIGURE 6-11 
-Refer to Figure 6-11. Block A has a mass of 3.00 kg and rests on a smooth table and is connected to block B, which has a mass of 2.00 kg, after passing over an ideal pulley, as shown. Block B is released from rest. How long does it take block B to travel 80.0 cm?
A) 0.404 s 
B) 0.494 s 
C) 0.639 s 
D) 0.785 s 
E) 0.935 s

Quizplus · Accepted Answer

The acceleration of the system is given by $a=\frac{m_2g-m_1g}{m_1+m_2}$. From the kinematic equation $x=ut+\frac{1}{2}at^2$, where $x=80\ 	ext{cm}$, $u=0$, and $a$ is found above, we can solve for $t$. Converting cm to m and plugging in the given values, we get $t = \sqrt{\frac{2x}{a}} = \sqrt{\frac{2(0.80)}{\frac{2}{5}(3+2)}} = 0.639\ 	ext{s}$, which gives us the correct answer of choice C.

FIGURE 6-11 -Refer to Figure 6-11. Block a Has a Mass of a Mass