1. A steam engine converts 150 kg of water completely to steam. The process involves transfer of 4 x 10^8 J as heat. If steam escaping through the safety valve does 2 x 10^8 J of work against outside atmosphere, the net change in the internal energy is:
a. 2 J
b. 2 x 108 J
c. 6 J
d. 6 x 108 J
2. A steam engine absorbs 4 x 10^5 J and expels 3.5 x 10^5 J in each cycle. What is its efficiency?
a. 100%
b. 12.5%
c. 75%
d. 33%
Thank you for the help! Physics is my hardest subject. :(
No problem, I'm here to help! Let's break down each question step by step:
1. The first question asks for the net change in internal energy in a steam engine process. To solve this, we need to consider the conservation of energy. The total change in internal energy is equal to the amount of heat transferred minus the work done by the steam escaping through the safety valve.
Given:
- Heat transferred (Q) = 4 x 10^8 J
- Work done by steam (W) = 2 x 10^8 J
The net change in internal energy (ΔU) can be calculated using the formula:
ΔU = Q - W
Plugging in the numbers:
ΔU = (4 x 10^8 J) - (2 x 10^8 J)
ΔU = 2 x 10^8 J
So, the net change in internal energy is 2 x 10^8 J, which corresponds to option (b) 2 x 10^8 J.
2. The second question asks for the efficiency of a steam engine. Efficiency is defined as the ratio of useful work output to the total energy input.
Given:
- Energy absorbed (Qin) = 4 x 10^5 J
- Energy expelled (Qout) = 3.5 x 10^5 J
The efficiency (η) can be calculated using the formula:
η = (Qout / Qin) * 100
Plugging in the numbers:
η = (3.5 x 10^5 J / 4 x 10^5 J) * 100
η = 0.875 * 100
η = 87.5%
So, the efficiency of the steam engine is 87.5%, which corresponds to option (c) 75%.
I hope this explanation helps you understand these physics concepts better! If you have any more questions, feel free to ask.