Explanation:
Given that,
Force acting on the child, F = 310 N
Length of the ropes, d = 2.1 m
We need to find the gravitational potential energy of the child–Earth system relative to the child's lowest position when the ropes are horizontal. The potential energy is simply given by :

Hence, this is the required solution.
A wheel and axle and an inclined plane.
Answer:
Vibrations of electric and magnetic fields.
Vibration of air particles
Vibration of the water particles.
Explanation:
We have here two groups of waves. Electromagnetic wave and mechanical waves.
- For the first one, electromagnetic waves, energy is transferred through vibrations of electric and magnetic fields.
- For the second group, mechanical waves as a sound, for instance, energy is transferred through vibration of air particles or particles of a solid through which the sound travels. Or In water waves, energy is transferred through the vibration of the water particles.
I hope it helps you!
We can do this with the conservation of momentum. The fact it is elastic means no KE is lost so we don't have to worry about the loss due to sound energy etc.
Firstly, let's calculate the momentum of both objects using p=mv:
Object 1:
p = 0.75 x 8.5 = 6.375 kgm/s
Object 2 (we will make this one negative as it is travelling in the opposite direction):
p = 0.65 x -(7.2) = -4.68 kgm/s
Based on this we know that the momentum is going to be in the direction of object one, and will be 6.375-4.68=1.695 kgm/s
Substituting this into p=mv again:
1.695 = (0.75+0.65) x v
Note I assume here the objects stick together, it doesn't specify - it should!
1.695 = 1.4v
v=1.695/1.4 = 1.2 m/s to the right (to 2sf)