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)