Jack asked in Science & MathematicsPhysics · 1 month ago

# What is the force applied on a magnetic bob falling through an aluminum tube?

Length of the tube = 1.45 m, time to fall through tube = 3.3 s, the scale which the tube is hanging from reads 825 g then once the magnet is inside it reads 855 g.

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• 1 month ago

The increase in the scale-reading is Δm = 855 - 825 = 30grams = 0.030kg.

This corresponds to an increase in force (ΔF = Δmg) on the aluminium tube of 0.030kg * 9.8 N/kg = 0.294N = 0.29N to two sig. figs.

So an additional force of 0.29N downwards has been applied to the tube by the falling magnet.  From Newton's 3rd law, the magnetic force applied to the magnet is 0.29N upwards. which I guess is the required answer.

(Note that the *total* force on the magnet is (magnet's weight - 0.29N).  But we don't know the magnet's weight so can only give the magnetic force (0.29N upwards).)

The distance and time are not used.

• NCS
Lv 7
1 month ago

By Newton's Third, the force on the bob is equal to the force on the tube:

F = (0.855 - 0.825)kg * 9.81m/s = 0.294 N