The number of oscillations of the toy in a second is 1.25.
<h3>What is frequency?</h3>
- This is the number of complete oscillation of an object is a given period.
The given parameter:
- Frequency of the toy, F = 1.25 Hz
The frequency of an object is calculated as follows;

where;
- n is the number of oscillations
- t is the time of motion
The number of oscillations of the toy in a second is calculated as follows;

Learn more about frequency here: brainly.com/question/10728818
Answer:
A) 
Explanation:
Since a = g - bv,
We can substitute a = dv/dt into the equation.
Then, the equation will be like dv/dt = g - bv.
So we got first order differential equation.
As known, v = 0 at t = 0, and v = g/b at t = ∞.
Since
⇒ 
So take the integral of both side.

Since for t=0, v = 0 ⇒ 

The density of aluminum is 2.7 g/ml.