buttercreem wrote:Please help with this question. Thank you.

These are the kinds of questions we go over with students during our September Holiday Program for End of Year Exam Revision (including IP) and O'Level Physics. I'm doing a lot of these problems with Sec 3 and Sec 4 students as well in our regular Physics tuition classes.

The answer is in two parts. For the first part, use a kinematics equation to solve for the initial velocity. We strongly recommend memorizing the 4 equations used for kinematics, as this is the fastest way of solving these kinds of problems.

For the second part, set the calculated kinetic energy = 95% of the actual kinetic energy. This needs to be done carefully. This little step at the end comes up in a lot of places in physics where efficiency is involved and it is important to think about the answer at the end. The actual initial velocity must be higher than the calculated initial velocity because energy was lost along the way.