The work done by the elephant to lift one log is the force multiplied by the height at which the log has been lifted: And so, the total work done to lift the 7 logs is 7 times the work done to lift each log:
Mercury is very harmful to the average human being. the mercury can easily be released from the lamp if the lamp is knocked over and broken. mercury is also harmful if inhaled. sodium on the other hand is not harmful in any way.