Two objects were lifted by a machine. one object had a mass of 2 kilograms and was lifted at a speed of 2m/sec. the other had a mass of 4 kilograms and was lifted at a rate of 3m/sec.

Sadly, after giving all the necessary data, you forgot to ask the question.
Here are some general considerations that jump out when we play with
that data:

For the first object:
The object's weight is (mass) x (gravity) = 2 x 9.8 = 19.6 newtons
The force needed to lift it at a steady speed is 19.6 newtons.
The potential energy it gains every time it rises 1 meter is 19.6 joules.
If it's rising at 2 meters per second, then it's gaining 39.2 joules of
     potential energy per second.
The machine that's lifting it is providing 39.2 watts of lifting power.
The object's kinetic energy is 1/2 (mass) (speed)² = 1/2(2)(4) = 4 joules.

For the second object:
The object's weight is (mass) x (gravity) = 4 x 9.8 = 39.2 newtons
The force needed to lift it at a steady speed is 39.2 newtons.
The potential energy it gains every time it rises 1 meter is 39.2 joules.
If it's rising at 3 meters per second, then it's gaining 117.6 joules of
     potential energy per second.
The machine that's lifting it is providing 117.6 watts of lifting power.
The object's kinetic energy is 1/2 (mass) (speed)² = 1/2(4)(9) = 18 joules.

If you go back and find out what the question is, there's a good chance that
you might find the answer here, or something that can lead you to it.

a) The graph of a normal curve with a mean of 64" and a standard deviation of 3.5" is a bell-shaped curve with its    

     maximum value at x = 64.

Important points:  

     mean - 3 deviations:     64 - 3(3.5)  =  64 - 10.5   =  53.5     

     mean - 2 deviations:      64 - 2(3.5)  =  64 - 7       =  57

     mean - 1 deviation:        64 - 3.5                           =  60.5

     mean:                                                                    =  64

     mean + 1 deviation:       64 + 3.5                           =  67.5  

     mean + 2 deviations:     64 + 2(3.5)  =  64 + 7       =  71           

     mean + 3 deviations:     64 + 3(3.5)  =  64 + 10.5  =  74.5  

 

b)  If there are 3000 plants, approximately how many will be taller than 71"?

     71"  is 2 standard deviations above the mean. The region between two standard deviations below the mean and two        standard deviations holds approximately 95% of the plants.

     Therefore there will be approximately 5% of the plants divided equally between being taller than two standard              

     deviations above the mean and being shorter than two standard deviations below the mean. Thus, there will be  

     approximately  2.5% of the plants taller than 71":  0.025 x 3000  =  75 plants.

Have a nice day :D