1. Marina, the acrobatic ballerina, is planning to dance along a wire stretched between two buildings. She wants the wire to be as straight as possible, because this fits the theme of her dance. She requires that the 10-meter-long wire not sag more than 1 cm when she is at the middle of the wire, and that the wire will not stretch at all. The building engineers are trying to explain that this will exert an enormous force on the buildings. Please help, by writing out an explanation in terms of the energy gravity provides as the wire sags, and the force the wire exerts at its ends.

2. In the third kind of lever, the force is applied between the fulcrum and the load. Explain what properties this kind of lever has: what is it good for?

3. Peter is lifting a 600 N box using a pulley system as shown. What force is he exerting to hold the box in place?
A. 1200 N
B. 600 N
C. 300 N
D. 200 N
E. 150 N