Someone is trying to balance a (110cm) plank with certain forces. a) Calculate the moment of the 60N force (about O), then name its type.

b) Calculate the moment of the 30N force (about O), then name its type

c) Will the plank balance? If not, which way will it tip?

d) What extra force would be needed at (B) to balance the plank?

Red light strikes a metal surface and electrons are ejected. if violet light is now used with a 10% greater intensity, what will happen to the ejection rate (number of ejected electrons per second) and the maximum energy of the electrons? a) greater ejection rate; same maximum energyb) same ejection rate; greater maximum energyc) greater ejection rate; greater maximum energyd) same ejection rate; same maximum energye) none of the above answers are correct

Explain what it means to view something from a frame of reference. provide an example that illustrates your explanation. (4 points)

Astone is thrown with a speed v0 and returns to earth, as the drawing shows. ignore friction and air resistance, and consider the initial and final locations of the stone. which one of the following correctly describes the change δpe in the gravitational potential energy and the change δke in the kinetic energy of the stone as it moves from its initial to its final location? options a.δpe = 0 j and δke = 0 j b.δpe is positive and δke is negative c.δpe = 0 j and δke is positive d.δpe is negative and δke is positive e.δpe = 0 j and δke is negative