Working
with units
1.
Find
out what is the radius (in m) and mass (in kg) of the earth. From the radius
calculate the volume of the earth assuming it’s a perfect sphere. Then
calculate the density of the earth in kg/m3.
radius of earth =
6378100m
mass of earth =
5.97219*1024 kg
volume of earth = à V=4/3 πr^3 àV = 1.086*1021
m3
density of earth = 5499.254 kg/m3
2.
A
car travels from Tel Aviv to Haifa a distance of 100km in 50 minutes. Assuming
the car moves at a constant speed, calculate the speed in m/s. (Change distance
to m and time to seconds)
distance = 100km
= 100000m
rate = 50 minutes
= 3000 seconds
speed = distance/rate = 33.33 m/s
3.
A
student riding on a bike, changes its speed from 1m/s to 3m/s over a period of
10 seconds. What is the acceleration including units. (Acceleration means the
change in speed per second)
Change in speed = 3m/s – 1m/s = 2m/s
Rate of change = 10s
Accelarion = change in speed / rate of change
Acceleration = (3-1)/10 = 2/10 = 0.2 m/s2
4.
A
satellite circles the earth once every hour and a half. Find the speed of the
satellite in m/s. (Assume the satellite revolves very close to the earth’s
surface.)
Circumference of earth = 2πr = 2*3.14*6378100 = 40054468m
Speed = distance/time = 40054468m/90minutes = 445049.64m/minutes =
7417.49m/s
5.
A
force of 200N accelerates a 20kg object from rest. What acceleration is it
causing? (Show also how you have obtained the units for your answer) (Remember:
Force = mass x acceleration.)
Force =
mass*acceleration à 200N = 20kg*acceleration à acceleration = 10N/kg
N = kgm/s2
à 10N/kg = 10m/s2
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