A runner runs the first 400m of a race in 80s, the second 400m in 70s and the final 800m in 130s. What was her average speed for
1 answer:
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(a) 198 g
When the rock is submerged into the water, there are two forces acting on the rock:
- its weight, equal to (m=mass, g=acceleration of gravity), downward
- the buoyant force, equal to (
=mass of water displaced), upward
So the resultant force, which is the apparent weight of the rock (W'), is
which can be rewritten as
where m' is the apparent mass of the rock. Using:
m = 540 g
m' = 342 g
we find the mass of water displaced
(b)
If the rock is completely submerged, the volume of the rock corresponds to the volume of water displaced.
The volume of water displaced is given by
where
is the mass of the water displaced
is the density of the water
Substituting,
And so this is also the volume of the rock.
(c)
The average density of the rock is given by
where
m = 540 g = 0.540 kg is the mass of the rock
is its volume
Substituting into the equation, we find
Explanation:
direction of electric field is same as that of force experienced by the test charge
