Answer:
0.66c
Explanation:
Use length contraction equation:
L = L₀ √(1 − (v²/c²))
where L is the contracted length,
L₀ is the length at 0 velocity,
v is the velocity,
and c is the speed of light.
900 = 1200 √(1 − (v²/c²))
3/4 = √(1 − (v²/c²))
9/16 = 1 − (v²/c²)
v²/c² = 7/16
v = ¼√7 c
v ≈ 0.66 c
(a). If the temperature of a substance is increased the density of it will also increased. The temperature is directly proportional to the density because the molecular activity of the substance will be affected by the temperature
(b).The mass of the substance doesn't at all. Because the amount of matter inside the substance cannot be affected by the temperature except that its water
The cyclist's final velocity is 10 m/s.
From the question,
We are to determine the cyclist's final velocity.
<h3>Linear motion</h3>
From one of the equations of motion for linear motion, we have

Where
v is the final velocity
u is the initial velocity
a is the acceleration
and t is the time
From the given information,
The cyclist starts at rest, this means the initial velocity is 0 m/s
That is,
u = 0 m/s
Also
a = 0.5 m/s²
and t = 20 s
Putting the parameters into the equation, we get



Hence, the cyclist's final velocity is 10 m/s.
Learn more on linear motion here: brainly.com/question/19365526