Answer:
Fusion fuels the buring of the sun.- second choice
The speed after 21 s is 18.9 m/s and the total time required for the train to reach a speed of 34 m/s is 14.4 s
<h3>
What is Speed ?</h3>
Speed is a distance travelled by a body per time taken. It is a scalar quantity and it is measured in m/s
Given that at Initially stationary, a train has a constant acceleration of 0.9 m/s2.
(a) What is its speed after 21 s?
- Acceleration a = 0.9 m/s²
Using v = u + at
Substitute all the parameters into the equation
v = 0 + 0.9 x 21
v = 18.9 m/s
(b) What is the total time required for the train to reach a speed of 34 m/s?
Let first calculate for total distance by using
v² = u² + 2as
34² = 18.9² + 2 × 0.9 × S
1156 = 357.21 + 1.8S
1.8S = 1156 - 357.21
1.8S = 798.79
S = 798.79 / 1.8
S = 443.8 m/s
v = u + at
34 = 21 + 0.9t
0.9t = 34 - 21
0.9t = 13
t = 13/0.9
t = 14.44s
Therefore, its speed after 21 s is 18.9 m/s and the total time required for the train to reach a speed of 34 m/s is 14.4 s
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Answer:
The speed of the raft is 1.05 m/s
Explanation:
The equation for the position of the stone is as follows:
y = y0 + v0 · t + 1/2 · g · t²
Where:
y = height of the stone at time t
y0 = initial height
v0 = initial speed
t = time
g = acceleration due to gravity
The equation for the position of the raft is as follows:
x = x0 + v · t
Where:
x = position of the raft at time t
x0 = initial position
v = velocity
t = time
To find the speed of the raft, we have to know how much time the raft traveled until the stone reached the river. For that, we can calculate the time of free fall of the stone:
y = y0 + v0 · t + 1/2 · g · t² (v0=0 because the stone is dropped from rest)
If we place the origin of the frame of reference at the river below the bridge:
0 m = 95.6 m - 9.8 m/s² · t²
-95.6 m / -9,8 m/s² = t²
t = 3.12 s
We know that the raft traveled (4.84 m - 1.56 m) 3.28 m in that time, then the velocity of the raft will be:
x/t = v
3.28 m / 3.12 s = v
v = 1.05 m/s
Answer:
Friction is useful in some cases like walking and cycling ..
but it is unwanted in machines as it create unwanted sounds and heat .,due to which we loss energy
Explanation:
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