A) Calculate the height of a cliff if it takes 2.35 s for a rock to hit the ground when it is thrown straight up from the cliff with an initial velocity of 8.00 m/s. B) How long would it take to reach the ground if it is thrown straight down with the same speed?

Explanation:

Given:

Using eq. of motion:

where:

distance travelled upwards to reach the top height

velocity at the top height during the motion = 0

Now the time taken to cover this displacement:

where

time taken to reach the top

Hence the time for which the rock travels down:

Now the displacement of the rock in the downward direction:

where:

total downward displacement

initial velocity for the course of downward motion

total time taken for the downward motion

So, the height of the cliff:'

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.

c)as speed changes, wavelength and frequency change.

everything changes!