**BMAT Prep Question Analysis - Q152 & Q109**

**Q152 A reaction is carried out in a container. A pure compound X is shown at the start of the experiment. Compound X undergoes a first order reaction to form compound Y, with no reverse reaction. **

**Which of the following might represent the container at 20 minutes? The diagram shows the number of molecules of each sample X and Y.**

** Q109 A car travels at a speed of 10 km/h and, upon seeing a road sign, it brakes and comes to a stop after 10 metres. If the car had initially been travelling at 100 km/h and it had decelerated at the same rate, how long would it have taken to come to a stop?**

a. 10m

b. 40m

c. 50m

d. 100m

e. 1000m

**Answer and Explanation**

**Q152 Answer:** B

**Explanation**: A first order reaction has a constant half-life. In the first 10 minutes, 15 molecules of compound X are transformed into compound Y. This represents 1 half-life. In the following 10 minutes, half of the remaining 15 molecules of compound X should turn into compound Y, giving a 7:23 split.

** Q109 Answer:** e. 1000m

**Explanation:** Use the equation v2= u?+2 as. We know that the final speed is 0 (as the car comes to a stop). Also the acceleration would be negative (since the car is decelerating), so we can simplify the equation to be u2=2 as. We can see that, by increasing the speed by a factor of 10, we get a 102 increase in distance. Thus the distance would be 1000 m.

Drafted by Quincy (BMAT Prep)