Answer: E) 80
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Step-by-step explanation:
We'll use the free fall formula, which is,
y = 0.5*g*t^2
where
- t = time in seconds
- g = acceleration of gravity (in m/s^2)
- y = vertical distance the object has fallen (in meters)
In this case,
- t = 4 seconds
- g = 10 m/s^2 approximately
Note: The freefall assumes the object is not thrown down, and simply dropped (so initial velocity is 0).
So,
y = 0.5*g*t^2
y = 0.5*10*4^2
y = 0.5*10*16
y = 5*16
y = 80
The object has fallen about 80 meters. This value is approximate because g = 10 is approximate. Use g = 9.81 for a more accurate value (though even then this value of g isn't exact either). In this case, your teacher has opted to use g = 10.
Another reason why 80 meters is an approximate value is because we haven't accounted for air resistance. As the object falls through the air, the air particles push up and resist the movement of the falling object, and therefore slow it down. Think of a parachute. For entry level physics courses, you'll ignore air resistance as it greatly complicates the problem. Though it's handy to keep it in mind for later physics courses down the road.