Hi there!
We can use Newton's Second Law:

∑F = net force (N)
m = mass (kg)
a = acceleration (m/s²)
We are given the mass and acceleration, so:
∑F = 20 · 2 = <u>40 N</u>
Answer:
2.5 m/s
Explanation:
The speed of the animal is given by the ratio between the distance travelled by the animal and the time elapsed:

where d is the distance travelled and t the time elapsed. Note that this quantity is also equal to the slope of the curve.
In the time interval 0-20 s, we have
d = 50 m - 0 m = 50 m
t = 20 s - 0 s = 20 s
So, the speed is

Answer:
16.4287
Explanation:
The force and displacement are related by Hooke's law:
F = kΔx
The period of oscillation of a spring/mass system is:
T = 2π√(m/k)
First, find the value of k:
F = kΔx
78 N = k (98 m)
k = 0.796 N/m
Next, find the mass of the unknown weight.
F = kΔx
m (9.8 m/s²) = (0.796 N/m) (67 m)
m = 5.44 kg
Finally, find the period.
T = 2π√(m/k)
T = 2π√(5.44 kg / 0.796 N/m)
T = 16.4287 s