—Are you sure you can do well in today’s test? ( )—_____________ I’ve got everything ready.
A:I’m afraid not.
B:I think so.
C:I hope not.
D:It’s hard to say.
点电荷A、B固定在真空中,所带电荷量均为q,若此时它们之间的库仑力为F,将两点电荷所带电量均变为﹣3q,则B球所受的库仑力将变成( )
____
下列各组物理量,在运算过程中都遵循平行四边形定则的是( )