The two blocks in (Figure 1) are connected by a massless rope that passes over a
ID: 1357479 • Letter: T
Question
The two blocks in (Figure 1) are connected by a massless rope that passes over a pulley. The pulley is15 cm in diameter and has a mass of 2.0 kg . As the pulley turns, friction at the axle exerts a torque of magnitude 0.60 Nm .
Part A
If the blocks are released from rest, how long does it take the 4.0 kgblock to reach the floor?
The two blocks in (Figure 1) are connected by a massless rope that passes over a pulley. The pulley is15 cm in diameter and has a mass of 2.0 kg . As the pulley turns, friction at the axle exerts a torque of magnitude 0.60 Nm .
Part A
If the blocks are released from rest, how long does it take the 4.0 kgblock to reach the floor?
Explanation / Answer
On 4kg block ( Fnet = ma)
4g - T1 = 4a ......(i)
On pulley (Torque = I *alpha)
T1r - T2r - 0.60 = (mr^2/2) (a/r)
T1 - T2 - 0.60 = 1a ..........(ii)
On 2kg block,
T2 - 2g = 2a ..... (iii)
addding (i), (ii) and (iii)
4g - 0.6 - 2g = (4 + 1+ 2)a
a = 2.72 m/s^2
Using H = ut + at^2 /2
1 = 0 + 2.72t^2 /2
t = 0.857 sec
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