Answer:
A
B

C

D

Explanation:
Considering the first question
From the question we are told that
The spring constant is 
The potential energy is 
Generally the potential energy stored in spring is mathematically represented as 
=>
=>
=>
Considering the second question
From the question we are told that
The mass of the dart is m = 0.050 kg
Generally from the law of energy conservation

=> 
=> 
Considering the third question
The height at which the dart was fired horizontally is 
Generally from the law of energy conservation

Here KE is kinetic energy of the dart which is mathematical represented as

=> 
=> 
=> 
Considering the fourth question
Generally the total time of flight of the dart is mathematically represented as

=> 
=> 
Generally the horizontal distance from the equilibrium position to the ground is mathematically represented as

=> 
=> 
Answer:
In most materials, as heat energy is absorbed, the density decreases. IF a certain object is heated, it might appear bigger than usual because it expands as the molecules inside moves faster than usual. However the mass of it stays the same while the density decreases.
<em><u>2</u></em><em><u>0</u></em><em><u>.</u></em><em><u>0</u></em><em><u>M</u></em><em><u>/</u></em><em><u>S</u></em><em><u>. </u></em><em><u> </u></em><em><u> </u></em><em><u> </u></em><em><u> </u></em><em><u>IS</u></em><em><u> </u></em><em><u>THE</u></em><em><u> </u></em><em><u>HORIZONTAL</u></em><em><u> </u></em><em><u>VELOCITY</u></em><em><u> </u></em><em><u>OF</u></em><em><u> </u></em><em><u>THE</u></em><em><u> </u></em><em><u>BALL</u></em><em><u> </u></em><em><u>JUST</u></em><em><u> </u></em><em><u>BEFORE</u></em><em><u> </u></em><em><u>IT</u></em><em><u> </u></em><em><u>REA</u></em><em><u>CHES</u></em><em><u> </u></em><em><u>THE</u></em><em><u> </u></em><em><u>GROUND</u></em>
<em><u>1</u></em><em><u>2</u></em><em><u>.</u></em><em><u>2</u></em><em><u> </u></em><em><u>SECONDS</u></em><em><u> </u></em><em><u> </u></em><em><u> </u></em><em><u> </u></em><em><u> </u></em><em><u>IS</u></em><em><u> </u></em><em><u>THE</u></em><em><u> </u></em><em><u>APPROXIMATE</u></em><em><u> </u></em><em><u>TOTAL</u></em><em><u> </u></em><em><u>TIME</u></em><em><u> </u></em><em><u>REQUIRED</u></em><em><u> </u></em><em><u>FOR</u></em><em><u> </u></em><em><u>THE</u></em><em><u> </u></em><em><u>BALL</u></em>