Answer:
Explanation:
Given
Initial speed is u=V
Maximum height of Pebble is H
Deriving maximum height of Pebble and considering motion in vertical direction

where v=final velocity
u=initial velocity
a=acceleration
s=Displacement
Final velocity will be zero at maximum height


i.e. maximum height is dependent on square of initial velocity
for twice the height

on comparing
The work done is 
Explanation:
The work done by a force on an object is given by:

where
F is the magnitude of the force
d is the displacement of the object
is the angle between the direction of the force and of the displacement
In this problem, we have
F = 1080 N is the force applied on the car
d = 218 m is the displacement of the car
And assuming the force is applied parallel to the motion of the car,
, and so the work done is

Learn more about work:
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The answer is (A) the object must be at rest.
When all of the forces acting on an object balance, the net force is zero and hence the object will not move.
Yes, the direction might also change under some special circumstances.