An electric motor drawing 15 kW and with an efficiency of 85% lifts a 400 kg crate B with...

An electric motor drawing 15 kW and with an efficiency of 85% lifts a 400 kg crate B with a constant speed vc. Pulley A has radius rp = 15 cm, and the center of mass of A is also the center of A. The cord is inextensible and does not slip relative to the pulley. Assume that the friction at the pulley bearings results in a moment about the pulley’s center with magnitude β| ωp| opposing the rotation of the pulley, where is β constant and |ωp| is the angular speed of the pulley. Hint: Review Example 4.16. Also note that friction in the pulley bearings causes the tension in the cord to be different on the two sides of the pulley.

Determine vc if β= 2kg·m2/s.

Figure P8.24

Example 4.16

EXAMPLE 4.16 Assessing Lift Speed Given the Efficiency