Answer:
0.91 J
Explanation:
The kinetic energy of an object is given by
where
m is the mass of the object
v is its speed
For the lemming in this problem, when he jumps, we have:
m = 0.0780 kg is the mass
v = 4.84 m/s is the speed
Substituting into the equation, we find:
The brightness of the lamp is proportional to the current flowing through the lamp: the larger the current, the brighter the lamp.
The current flowing through the lamp is given by Ohm's law:
where
V is the potential difference across the lamp, which is equal to the emf of the battery, and R is the resistance of the lamp.
The problem says that the battery is replaced with one with lower emf. Looking at the formula, this means that V decreases: if we want to keep the same brightness, we need to keep I constant, therefore we need to decrease R, the resistance of the lamp.