7 A. second law is F=ma so is force is 0 then a is 0 therefore if an object is at rest it will remain at rest, and it is moving at a constant speed it will remain moving at a constant speed which is the first law
15 it's height decreases by h/2 and its mass also decreases by m/2 so P.E loss is m/2*h/2*g=mgh/4 which is B
18 initially height are the same, pressure is the same at both sides at it is equal to atmospheric pressure. an change in pressure will be due to change in pressure of the gas. So one side decreases by h and the other side increases by h also. so the total change in height is 2h. pressure increase in the flask is there 2hpg D
20 since they are the same materials, they have the same young modulus and since they are being strectched to the same extension, you need to use 1/4 the force you use on P to get the same extension in q so 1/0.25= 4
29 D. when it enter the magnetic field, it experiences a force of Ee. this force is acting in the opposite direction to the velocity so the electron is decelerating. using linear motion equation, v2=u2-2as, where a is F/m that is Ee/m and u is v, and s is x, making x the subject you get mv2/2Ee
