Answer: Magnetic and gravitational force
Explanation: When a magnet and an iron nail are kept at a distance,the magnet attracts the nail without touching using magnetic force. In this example, the magnet and the nail are interacting.
The earth pulls the moon towards it and keeps it in orbit without touching it, using gravitational force. In this example,the moon and the earth are interacting.
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15+3=18km/hour
Think about it like this. The boat is going 15 faster than the river, and the river is going 3 faster than the bank, so the boat is going 18 faster than the river bank
Answer:
Frequency, 
Explanation:
Visible red light has a wavelength of 680 nanometers (6.8 x 10⁻⁷ m). The speed of light is 3.0 x 10 ⁸ m / s. What is the frequency of visible red light?
It is given that,
Wavelength of a visible red light is, 
Speed of light is, 
We need to find the frequency of visible red light. It can be calculated using below relation.

So, the frequency of visible red light is
.
The velocity of penguin as he ends where he started was 0 m/s.
<h3>What is displacement?</h3>
Displacement is the length of straight line joining the initial and final position of the body.
Given is a penguin who waddled 8 m uphill before sliding back down to its friends in 2 seconds.
We know that the velocity is the rate of change of displacement with respect to time. Mathematically -
v = dx/dt
dx = v dt
∫dx = ∫v dt
Δx = vΔt
v = Δx/Δt
Now, the displacement of the penguin will be = Δx = 8 - 8 = 0
Then, its velocity will be -
v = 0/Δt = 0
Therefore, the velocity of penguin as he ends where he started was 0 m/s.
To solve more questions on kinematics, visit the link below-
brainly.com/question/27200847
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