you measure acceleration of two masses attached to a string threaded over a pull

Question

you measure acceleration of two masses attached to a string threaded over a pulley at 4.9 m/s^2. Which of the following must be the value of the two masses?

a) 0 grams &300 grams

b) 50 grams & 300 grams

c) 100 grams & 300 grams

d) 150 grams & 300 grams

You notice that the pulley being used in the lab has noticeable friction. What effect does this friction have on the acceleration of the masses?

a) friction makes the masses acceleration more slowly

b) friction makes the masses accelerate more quickly

c) pulley friction has no effect

d) the friction causes the masses to not move at all.

Explanation / Answer

1) Let the masses be M1 and M2

If M1<M2 then the tension in the string is M1*g

and M2g- M1*g = M2 *g/2 (since newton's 2nd law of motion)

---> M2 - M1 = M2 /2

M2/2 = M1

M2 = 2 *M1

Hence the weights are d)150 g and 300g

2) a) Friction causes the masses to acclerate more slowly

the reason being

Due to the law of conservation of energy, the kinetic energy would be converted into heat energy as the two surfaces rub together therefore slowing the mass down.

T = mg + F , therefore there would be a higher tension in the rope.

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