C. 32400 because 540 * 60 = 32400
The answer is that the reverse arrows pointing to the left needs to release energy. The molecules in the gas state are free such that they can travel from one point to another easily. They have the highest amount of energy. So, if you want the molecules to come closer together, you need to remove the energy to keep them in place. Therefore, the arrows pointing to the right require removal of energy.
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)
FBD provides a visual for every force that the object experiences. It can tell you the direction by showing the direction and magnitude of the forces. You can calculate the net force, example being that the applied force is 300N and the force of friction is 100N, the net force is 200N in the direction of the applied force. (Fnet= Fa- Ff).
Rock is completely immersed in hot water. By the second law of thermodynamics, thermal energy or heat is transferred from substance with higher temperature to substance with lower temperature until they come to thermal equilibrium i.e. both at same temperature.
It is given here that rock is at 20°C which is at lower temperature than water at 80°C. ∴Heat or thermal energy flows from water to rock. So, right choice is-
A. The water gives the rock thermal energy and gets no thermal energy in return.
