Which action would further decrease the reading on the balance?

Answer: Option D

Refer to the video for the explanation

Which action would further decrease the reading on the balance? https://youtu.be/VTwZrLiCHVE

Where must the observer position himself so he will be able to see the image of O in the mirror?

Answer: Option A

For such questions, always locate accurately the position of the image of the O. Then draw the ray from the image to the observer. To determine the maximum scope of view using the mirror, always use the two extreme edges of the mirror as point of incidences.

Where must the observer position himself so he will be able to see the image of O in the mirror? https://youtu.be/zE12AogL728

SP2017P1Q8 What is the minimum speed the golf ball must have at X to reach Y?

Answer: Option D

The most common mistake is to equate total energy at X equals to total energy at Y. At Y, there is no way to know the speed as the speed varies which depends on the speed at X.

Since the question wants to find the minimum speed at X to reach Y, you should focus on the highest point of the hill. If you can just clear the hill, you will sure reach Y. So you should consider the total energy at the highest point of the hill and assume the ball just barely reaches the top and stops there. Hence at the highest point, the energy of the ball is just GPE and you can find the minimum speed at point X. Any speed higher, you can clear the hill and reach Y.

SP2017P1Q8 What is the minimum speed the golf ball must have at X to reach Y? https://youtu.be/bFKlM7vOVbI