Centripetal force

[fterh]

Found this question online: A ball with a mass of 250 g has a centripetal acceleration of 5 m/s2. What is the centripetal force acting on this ball?

 

My calculation is 0.25 * 5 = 1.25N, but the answer is 1250N. I think the answer is wrong (because I believe all calculations should be done in SI units), but I just want to verify. I'd appreciate if you guys use simpler terms, because I'm in secondary 4 (high school equivalent) and this stuff is beyond my level (it's for Physics Olympiad).

 

Thanks!

[timo]

My calculation is 0.25 * 5 = 1.25N,...

Surely you meant [math] 0.25 \text{ kg} \cdot 5 \frac{\text{m}}{\text{s}^2} = 1.25 \text{ N}[/math] - the units absolutely belong to the calculation in every step. This result should be correct.

 

... but the answer is 1250N. I think the answer is wrong (because I believe all calculations should be done in SI units), but I just want to verify.

1) 1250 N is wrong, your answer should be fine.

2) Check if the answer sheet possibly said [math]1250 \frac{\text{g m}}{\text{s}^2}[/math] which might be easily mistaken for [math]1250 \frac{\text{kg m}}{\text{s}^2}[/math].

3) While it is a good idea to do all calculations in SI units it is not strictly necessary. As long as you are carrying around your units in every step the actual choice of units does not matter. But just staying in SI is also fine if you have trouble understanding the reason.