when an athlete presses a 115kg barbell from his chest to a distance of 0.71m above his chest, he does blank of work

Agroup of students is studying convection currents. they fill two identical balloons with the same amount of helium. one balloon is placed in a freezer and the other in an area with warm air. after 10 minutes, the balloons are released from a height of 1 meter. which of the following do the students most likely observe? question 2 options: the balloons rise at the same rate. both balloons are the same size. the ballons both rise. the cold ballon is larger than the warm balloon. the cold balloon expands and rises. the warm balloon shrinks and sinks. the warm balloon expands and rises. the cold balloon shrinks and sinks.

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.

At what time will the interfering waves have an amplitudeof zero?