Answer:
oo.p i wish I could answer that
Explanation:
Answer:60 gm
Explanation:
Given
initial velocity of ball 
Force exerted by racquet 
time period of force 
final velocity of ball 
Racquet imparts an impulse to the ball which is given by



The answer is B (The second one). I'm not sure though.
A decrease in it's operating temperature would make a heat engine less efficient. This is because in order to operate, a heat engine needs to be hot and maintain that temperature.
Https://www.slideshare.net/mobile/jan_parker/life-cycle-of-stars-3196871
the answer to your question!