The first one is C. Hope this helps!! If you need anymore help just message me and I will try to get back to you quickly and help in any way i can!
Answer:

Explanation:
Given
,
,
,
The tension of the spring is



The force in the spring is equal to centripetal force so


But Fc is also
Fc=KxΔr

Replacing



total distance is

Acceleration = velocity/time
A= 3.5m/s/15s
A= 0.23m/s^2
Answer:
A 1.0 min
Explanation:
The half-life of a radioisotope is defined as the time it takes for the mass of the isotope to halve compared to the initial value.
From the graph in the problem, we see that the initial mass of the isotope at time t=0 is

The half-life of the isotope is the time it takes for half the mass of the sample to decay, so it is the time t at which the mass will be halved:

We see that this occurs at t = 1.0 min, so the half-life of the isotope is exactly 1.0 min.