One fine summer day a group of students was jumping from a railroad bridge into the river
below. they stepped off the bridge with an acceleration (due to gravity) of 9.8 and they hit the
water 4.0 s later. how high (in meters) was the bridge?

78.4 m

Explanation:

This problem is a good example of Vertical motion, where the main equation for this situation is:  

(1)  

Where:  

is the height of the jumpers

is the initial height of the jumpers

is the initial velocity of the jumpers  

is the time at which the jumpers reach the water

is the acceleration due to gravity  

Having this clear, let's find from (1):

(2)  

(3)  

Finally:

 This is the height of the bridge

depends on what you mean by "group." for order, it would be coleoptera (beetles). for class, it would be insecta (insects). for phylum, it would be the arthropoda (animals with jointed exoskeletons).

explanation:

multiply 2kg by latent heat of vap