Heat engines are less than 100% efficient because absolute zero cannot be reached
Answer: Answer to the I'm Tall when I'm Young, and I'm Short when I'm Old. What am I? Riddle is a candle
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Answer:
The deceleration is
Explanation:
From the question we are told that
The distance of the car from the crossing is 
The speed is 
The reaction time of the engineer is 
Generally the distance covered during the reaction time is

=> 
=> 
Generally distance of the car from the crossing after the engineer reacts is
=>
=> 
Generally from kinematic equation

Here v is the final velocity of the car which is 0 m/s
So

=>
Answer:
The velocity of Dan is 1.13 m/s.
Explanation:
Given that,
Initial velocity of skateboard and Dan = 2.00 m/s
Velocity of skateboard = 7.00 m/s
Mass of Dan m= 40.0 kg
Mass of skateboard M= 7.00 Kg
Suppose How fast is Dan going as his feet hit the ground?
We need to calculate the initial velocity of Dan
Using conservation of momentum

Put the value into the formula



Hence, The velocity of Dan is 1.13 m/s.