The unit of length most suitable for measuring the thickness of a cell phone is a . the unit of length most suitable for measuring the height of a backyard tree is a .

Millimeter and meter

Explanation:

Cellphones are only a few millimeters in thickness.

It is easier to say 5 millimeter than 0.0005 meter.

The unit we use must help others easily visualize and understand the size of the object.

a 5 millimeter is easy to visualize than a 0.0005 meter or a 5,000,000 nano meter

In the same way, a tree in our backyard usually grow as tall as a few meters. ( remember trees in amazon forest might grow as tall as a few kilometers). so in the case of trees in our home the right unit to measure them is meters.

5 w for 1hr = 5x60x60 joules=300x60=3000x6=18,000j as total energy conversion. efficiency of bulb needed for radiant to thermal within 18000

can be answered using momentum.

momentum = p

p1= mass1 * velocity1

p1 = p2

therefore

p1 = 6kg * 4m/s

p1 = 24kgm/s

p2=m2 * v2

24 kgm/s = 7kg * v2

v2 = 24 kgm/s / 7kg

v2= 3.42 m/s