Physics Review Question

Unit: mechanics
Year: 1994 Question#: 12
Question: A net force of 5.0 x 102 newtons causes an object to accelerate at a rate of 5.0 meters per second2. What is the mass of the object?

(1 ) 1.0 x 102 kg
(2 ) 2.0 x 10-1 kg
(3 ) 6.0 x 102 kg
(4 ) 2.5 x 103 kg

What is this question really asking?

Explanation by: Lindsay K

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Answer 1
1) 1.0 x 102 kg


Find the acceleration that contains weight, acceleration, and and mass: Fnet = ma. Then simply plug in numbers to find the unknown mass:
(5.0 x 102 newtons is really 500newtons) 500 newtons = (5m/s)(m) 500 newtons/5m/s = m 100 kg = m and 100kg in scientific notation is 1.0 x 102 kg So this is the correct mass of the object.

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Answer 2
2) 2.0 x 10-1 kg


2 x 10-1 kg is really .2 kg, and this is really too small. Try using the correct formula of Fnet = ma

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Answer 3
3) 6.0 x 102 kg


6.0 x 102 kg is 600 kg, and it does not make sense, it is too big to be the mass. Try using the correct formula of Fnet = ma

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Answer 4
4) 2.5 x 103 kg


You can not just multiply 5.0 x 102 kg (which is really just 500kg) by 5 m/s, that's not how the formula works. ((500kg)(5m/s) = 2500Newtons NO! DO NOT DO THIS - does not follow the formula).

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What's this question really asking?

Do you know how to use the formula Fnet = ma, and do you know how to work with scientific notation.

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