Answer:
(a) 
(b) 
(c) 
Explanation:
(a) According to Newton's second law, the acceleration of a body is directly proportional to the force exerted on it and inversely proportional to it's mass.

(b) According to Newton's third law, the force that the sled exerts on the girl is equal in magnitude but opposite in the direction of the force that the girl exerts on the sled:

(c) Using the kinematics equation:

For the girl, we have
and
. So:

For the sled, we have
. So:

When they meet, the final positions are the same. So, equaling (1) and (2) and solving for t:

Now, we solve (1) for 

The movement of a fluid during convection is a circular/oval motion since the fluid at the top sinks and the fluid at the bottom rises.
Hope this helps :)
Answer: a) B = 6811N
b) m = 603.2kg
c) 86.8%
Explanation: <em>Buoyant force</em> is a force a fluid exerts on a submerged object.
It can be calculated as:

where:
is density of the fluid the object is in;
is volume of the object;
g is acceleration due to gravity, is constant and equals 9.8m/s²
a) For the hollow plastic sphere, density of water is 1000kg/m³:

B = 6811N
b) Anchored to the bottom, the forces acting on the sphere are <u>Buoyant</u>, <u>Tension</u> and <u>Force due to gravity</u>:
B = T + 
B = T + mg
mg = B - T

Calculating:

m = 603.2kg
c) When the shpere comes to rest on the surface of the water, there are only <u>buoyant</u> <u>and</u> <u>gravity</u> acting on it:
B = m.g



= 0.6032m³
Fraction of the submerged volume is:
=
= 0.868
<u />
Time required : 25.876 s
<h3>Further explanation</h3>
Given
A car weight = 25000 N
Brake force = 628 N
vo= 6.5 m/s
vt = 0(stop)
Required
time to stop
Solution
W = m . g
25000 = m.10
m=2500 kg
Newton's second law
F = m . a
628 = 2500 . a

vt=vo-at(deceleration a=-)
0=6.5-0.2512.t
0.2512.t=6.5
t=25.876 s