Aspeed trap is set up with two pressure-activated
stripsplaced across a highway, 110 m apart. a car is speeding
alongat 33m/s, while the speed limit is 21 m/s. at the instant
thecar activates the first strip, the driver begins slowingdown.
what minimum deceleration is needed in order that theaverage speed
is within the limit by the time the car crosses thesecond
marker?

a = 0.21 m/s²

Explanation:

The average speed measured by the strip system is:

We need time T to be such that v < (21m/s). So we must find the acceleration a such that:

We are dropping units for simplicity. Time is always seconds and distance meters.

Lets call x to car position, being x=0 at the first strip. The movement with constant acceleration is:

We take a negative acceleration because the car must be slowing down.

At time t = 110/21 we need x = 110:

So, the minimum acceleration is a = 0.21 m/s²

d is the correct answer

gas and liquid