| Q: A ball of mass M is spun in a circle at the end of a string of length R. If both M and R double, what would happen to the centripetal force if velocity of the ball remains the same? |
| A | become one-quarter of previous | |
| B | become one-half of previous | |
| C | double | |
| D | remain the same |
The correct answer is D. For this question, we should recall the equation for centripetal force:
We can start from Newton’s second law, F = ma, and recall that centripetal acceleration is v^2/r. So in this case, if both m and r double, but v stays the same, the doubling cancels, and F remains the same. For example, 2*constant/3 is the same as 4*constant/6.