1. what is the average acceleration of a subway train that speeds up from 9.6m/s to 12m/s in .8s on a straight track?
2. an acorn at rest falls from an oak tree. the acorn hits the ground with a velocity of 14.7m/s. how long did it take the acorn to land?
3. what force is necessary to accelerate a 1,250 kg car at a rate of 40m/s^2
4. the mass of a person that weighs 500 n is
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Explanation:

1. Average acceleration is change in velocity over change in time.

a = Δv / Δt

a = (12 m/s - 9.6 m/s) / 0.8 s

a = 3 m/s²

2. a = Δv / Δt

9.8 m/s² = (14.7 m/s - 0 m/s) / Δt

Δt = 1.5 s

3. Force is mass times acceleration.

F = ma

F = (1250 kg) (40 m/s²)

F = 50,000 N

4. F = ma

500 N = m (9.8 m/s²)

m ≈ 51 kg

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.