# Velocity and differential equation

#1
Hello. Can someone tell me what they mean for d) I don’t understand this because I didn’t take physics so my knowledge in it is very dim and in the exams are we ever asked to elaborate and explain stuff like this?
Last edited by Eris13696; 9 months ago
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9 months ago
#2
Sure, an explain could be a question part. So as the solution says, what is dv/dt when v=60? What does it mean if the acceleration (dv/dt) is negative?
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#3
(Original post by mqb2766)
Sure, an explain could be a question part. So as the solution says, what is dv/dt when v=60? What does it mean if the acceleration (dv/dt) is negative?
the answer is negative, and because negative in physics it means the acceleration is slowing down right, what about the air resistance part :0?
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9 months ago
#4
(Original post by Eris13696)
the answer is negative, and because negative in physics it means the acceleration is slowing down right, what about the air resistance part :0?
negative acceleration means the speed is decreasing. It starts at v=60, but terminal speed is 50, so the speed must decrease from 60 to 50.

The acceleration
dv/dt = 10 - 0.2v
has two parts gravity (10) and air resistance (-0.2v). Newton 2 means that the total force (acceleration) is the sum of the two forces. Gravity generates a positive constant acceleration, air resistance is negative (it opposes motion) and is proportional to the speed.

gcse physics covers all you need to know about the interpretation.
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#5
(Original post by mqb2766)
negative acceleration means the speed is decreasing. It starts at v=60, but terminal speed is 50, so the speed must decrease from 60 to 50.

The acceleration
dv/dt = 10 - 0.2v
has two parts gravity (10) and air resistance (-0.2v). Newton 2 means that the total force (acceleration) is the sum of the two forces. Gravity generates a positive constant acceleration, air resistance is negative (it opposes motion) and is proportional to the speed.

gcse physics covers all you need to know about the interpretation.
If I’m honest I dropped physics since igcse because it’s not my strong points but thank you for the explanation, I really appreciate your help!!
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