(a) The ball's height <em>y</em> at time <em>t</em> is given by
<em>y</em> = (20 m/s) sin(40º) <em>t</em> - 1/2 <em>g t</em> ²
where <em>g</em> = 9.80 m/s² is the magnitude of the acceleration due to gravity. Solve <em>y</em> = 0 for <em>t</em> :
0 = (20 m/s) sin(40º) <em>t</em> - 1/2 <em>g t</em> ²
0 = <em>t</em> ((20 m/s) sin(40º) - 1/2 <em>g t</em> )
<em>t</em> = 0 or (20 m/s) sin(40º) - 1/2 <em>g t</em> = 0
The first time refers to where the ball is initially launched, so we omit that solution.
(20 m/s) sin(40º) = 1/2 <em>g t</em>
<em>t</em> = (40 m/s) sin(40º) / <em>g</em>
<em>t</em> ≈ 2.6 s
(b) At its maximum height, the ball has zero vertical velocity. In the vertical direction, the ball is in free fall and only subject to the downward acceleration <em>g</em>. So
0² - ((20 m/s) sin(40º))² = 2 (-<em>g</em>) <em>y</em>
where <em>y</em> in this equation refers to the maximum height of the ball. Solve for <em>y</em> :
<em>y</em> = ((20 m/s) sin(40º))² / (2<em>g</em>)
<em>y</em> ≈ 8.4 m
Well depending on the speed of both of those things is were the rock will be placed and it also determines how fast can an environment change
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Answer:
Explanation:
Given
Each student exert a force of 
Let mass of car be m
there are 18 students who lifts the car
Total force by 18 students 
therefore weight of car 
mass of car 

(b)
Answer:
The value is 
Explanation:
From the question we are told that
The mass of the ice cube is 
The temperature of the ice cube is
The mass of the copper cube is 
The final temperature of both substance is 
Generally form the law of thermal energy conservation,
The heat lost by the copper cube = heat gained by the ice cube
Generally the heat lost by the copper cube is mathematically represented as
![Q = m_c * c_c * [T_c - T_f ]](https://tex.z-dn.net/?f=Q%20%3D%20%20m_c%20%20%2A%20%20c_c%20%2A%20%20%5BT_c%20%20-%20%20T_f%20%5D)
The specific heat of copper is 
Generally the heat gained by the ice cube is mathematically represented as

Here L is the latent heat of fusion of the ice with value 
So

=>
So
=> 