Step-by-step explanation:
for the car question
the answer is
that the box on the roof will slip forward when the car hits the wooden box
because the box on the car roof is in motion
when the car hit the wooden block
the wooden block will try to stop the car
due to which the speed of the car will be decelerated but the box will try to continue its motion so it will move forward due to inertia of the box
and the answer for the 2nd question is that
the sand bucket will provide more resistance to the change in motion because along with the bucket the sand will also try to not change their state of rest so due to their inertia the sand bucket will provide more resistance than the simple bucket