The work done against gravity is 100 J
Explanation:
The work done against gravity in order to lift an object is equal to the change in gravitational potential energy of the object:

where
m is the mass of the object
g is the acceleration of gravity
is the change in height of the object
For the object in this problem, we have:
m = 5 kg


Substituting into the equation,

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The velocity of the boy when he hits the water at the bottom of the slide is 14 m/s.
<h3>
Velocity of the boy at the bottom of the slide</h3>
The velocity of the boy when he hits the water at the bottom of the slide is calculated from the principle of conservation of energy.
K.E = P.E
¹/₂mv² = mgh
v² = 2gh
v = √2gh
where;
- h is height of the boy
- g is acceleration due to gravity
v = √(2 x 9.8 x 10)
v = 14 m/s.
Thus, the velocity of the boy when he hits the water at the bottom of the slide is 14 m/s.
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The book continue to move due to its inertia
Explanation:
We can answer this question by using Newton's first law, which states that:
"When an object is moving with constant velocity (or it is at rest), it will continue moving with constant velocity (or will stay at rest) unless acted upon an external unbalanced force".
This law is also known as law of inertia.
If we apply this law to the situation in the problem, we notice that:
- Before the car stops, the book is moving with constant velocity (25 mph) together with the car
- When the car stops, there are no external forces acting on the book, which is free to continue its motion: so, the book will continue moving at 25 mph forward, due to its inertia. The book will be eventually stopped when it hits the floor (because the floor applies an unbalanced force on it).
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