Phy MC Questions

15. Option C

Use s = ut + (1/2)at^2
Because the ball is released from rest, u = 0 m/s, and a = g
thus s = (1/2)gt^2
Work done W = force x displacement = (mg).s = (mg^2/2).t^2
i.e. W varies with the square of time t

33. Option B
Apply Fleming's Left Hand Rule.

19. Option A.
The -ve charge moves against the direction of the field lines set up by the +ve charge.

17. Option B
Since g = GM/r^2
where g is the acceleration due to gravity (or gravitational field strength)
G is the Universal Gravitational Constant
M is the mass of the earth
r is the distance from earth centre

Hence, field strength at earth surface g = GM/R^2
where R is the earth radius
i.e. GM/R^2 = 10 N/kg

Field strength at moon's distance g' = GM/(30R)^2 = (1/900).GM/R^2 = 10/900 N/kg
hence, g' = 1/90 N/kg = 0.011 N/kg = 11 mN/kg