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A Level Forces And Newtons Laws Question

A ball of mass 200g falls vertically through a container of oil at a constant speed of 3m/s. Calculate the resistance on the ball bearing from the oil.

I did:
F - R = ma
F - R = 200 x 3
F - R = 600

But I don't know what to do next to get the resistance. Please could someone give me a pointer as to what to do next, thanks in advance!
Original post by Shadow_12
A ball of mass 200g falls vertically through a container of oil at a constant speed of 3m/s. Calculate the resistance on the ball bearing from the oil.

I did:
F - R = ma
F - R = 200 x 3
F - R = 600

But I don't know what to do next to get the resistance. Please could someone give me a pointer as to what to do next, thanks in advance!


The ball is falling through the oil at a constant speed. i.e. it has reached terminal velocity. That means it is no longer accelerating and therefore the gravitational force acting on the ball is in equal and opposite equilibrium with the resistive force (drag).

Fgrav + Fres = 0

mg + Fres = 0

Fres = -mg

Fres = -0.2kg x 9.81m/s

Fres = -1.96N
(edited 5 years ago)
Original post by uberteknik
The ball is falling through the oil at a constant speed. i.e. it has reached terminal velocity. That means it is no longer accelerating and therefore the gravitational force acting on the ball is in equal and opposite equilibrium with the resistive force (drag).

Fgrav + Fres = 0

mg + Fres = 0

Fres = -mg

Fres = -0.2kg x 9.81m/s

Fres = -1.96N


Thank you so much!! Maybe this is just me being stupid but why is it Fgrav + Fres = 0? Would it not be Fgrav - Fres = 0 (because the 2 forces are the same and if you subtract them then would make 0)?

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