# Evan's Space

## Time interval between two sounds from a gun – direct and reflected sound

Solutions: Option B

You can view the video tutorial here or the written solutions below.

## Minimum force F to push barrel up a step

Solutions: Option D

You can view the video tutorial here or the written solutions below.

## 2013SPp1q17 What is the new P when V across resistor is doubled?

Solutions: C

Alternatively, you may put values to work out using the 2 basic formulae of P = IV and V = IR. Refer the video below.

## What is the speed-time graph of the object when pulling force is removed?

A constant horizontal force F, of magnitude 16 N, is applied to an object at rest on a rough surface. The constant force of friction is 8 N. At X, the force F is removed.

Which speed-time graphs correctly shows the motion of the object?

Solutions: Option B

Either B or D is correctly. But you need to find the magnitude of the deceleration after X in order to determine if the magnitude (gradient) is greater or smaller than the magnitude of the acceleration before X.

## Ratio of masses of same substance when heated

Two blocks X and Y, which are made of the same metal, are heated by heaters of the same power rating. The variation of temperature with time of both blocks is shown on the same graph below.

What is the ratio of the mass of X to that of Y?

A   1 : 3          B   1 : 4         C   3 : 1        D   4 : 1

Option: B