A pendulum makes 60 vibrations in 15 secs what's its frequency

4 hertz

Explanation:

The defination of freqyency = the total no of cycle made by a wave in one second.

so,

cycle or vibrations=60

tame taken = 15

now,

frequency = no. of cycle / time taken

= 60/15

=4 hertz

hence, the its frequency = 4hertz