Two weights are connected by a massless wire and pulled upward with a constant speed of 1.50 m/s by a vertical pull P.The tension in the wire is T (see figure).P is closest to
A)25 N.
B)125 N.
C)187.5 N.
D)245 N.
E)1225 N.

Question

Two weights are connected by a massless wire and pulled upward with a constant speed of 1.50 m/s by a vertical pull P.The tension in the wire is T (see figure).P is closest to 
A)25 N. 
B)125 N. 
C)187.5 N. 
D)245 N. 
E)1225 N.

Quizplus · Accepted Answer

The tension in the wire is equal to the weight of the two masses, which is given by $T=mg_1+mg_2$, where $g_1$ and $g_2$ are the gravitational accelerations of the two masses. Since they are being pulled upward at a constant speed, the net force on them is zero, which means that the upward force from the tension in the wire is equal to the downward force of gravity. Therefore, we have $P=T=mg_1+mg_2$, where $m$ is the mass of each weight. Substituting $m=10$ kg and $g=9.8$ m/s$^2$, we get $P=2m g=196$ N. The closest choice is B, 125 N.

Two Weights Are Connected by a Massless Wire and Pulled