<u>Answer:</u> The voltage needed is 35.7 V
<u>Explanation:</u>
Assuming that the resistors are arranged in parallel combination.
For the resistors arranged in parallel combination:

We are given:

Using above equation, we get:

Calculating the voltage by using Ohm's law:
.....(1)
where,
V = voltage applied
I = Current = 3.75 A
R = Resistance = 
Putting values in equation 1, we get:

Hence, the voltage needed is 35.7 V
Answer:1200 kg
Explanation:
Given
Electromagnet can lift a mass of 
Magnetic force necessary to hold mass is proportional to Magnetic field
and magnetic field (B) is proportional to NIA
where N=no of turns
I=current in the magnet
A=area of cross-section
When we double the no of turns and triple the current then
N becomes 2 N
I becomes 3 I
therefore magnetic field becomes 6 times
Thus magnetic force becomes 6 times and we can say that electromagnet can hold the 6 times of given weight
i.e. 
Answer:
efficiency = 5.4%
Explanation:
Efficiency of heat engine is given as

now we will have

so we will have

now we know that

so we have



so efficiency is 5.4%
Last one: Every object in the universe attracts every other object