উড়োজাহাজ থেকে নিক্ষিপ্ত বোমা মাঝপথে ফেটে গেলে এর - 

A ball moving with a velocity v strikes a wall moving toward the ball with a velocity u. An elastic impact lasts for t sec. Then the mean elastic force acting on the ball is ;

A heavy ball moving with speed $v$ collides with a tiny ball. The collision is elastic, then immediately after the impact, the second ball will move with a speed approximately equal to-

A 50 gm ball collides with another ball of mass 150gm, moving in its direction of motion, After collision the two ;balls move at a an angle $30^{0}$ with their initial direction. Ratio of their velocities after collision is

একটি বল 60m উঁচু হতে মাটিতে পতিত হলে এটি 75% শক্তি হারিয়ে ফেললে এটি প্রতিফলিত হয়ে কত উচ্চতায় উঠবে?