It doesn't matter what the object's initial velocity is, or how long
the acceleration lasts. All that matters is the object's mass and
acceleration.
Force = (mass) x (acceleration) =
(5kg) x (15 m/s²) =
75 kg-m/s² = <em>75 newtons .</em>
Answer:

Explanation:
We are given that three resistors R1, R2 and R3 are connected in series.
Let
Potential difference across 
Potential difference across 
Potential difference across 
We know that in series combination
Potential difference ,
Using the formula

Hence, this is required expression for potential difference.
Answer:
Approximately
, assuming that the acceleration of this ball is constant during the descent.
Explanation:
Assume that the acceleration of this ball,
, is constant during the entire descent.
Let
denote the displacement of this ball and let
denote the duration of the descent. The SUVAT equation
would apply.
Rearrange this equation to find an expression for the acceleration,
, of this ball:
.
Note that
and
in this question. Thus:
.
Let
denote the mass of this ball. By Newton's Second Law of Motion, if the acceleration of this ball is
, the net external force on this ball would be
.
Since
and
, the net external force on this ball would be:
.