It might have a caliper sticking, or worn brake pads. This can also be caused by bad ball joints. If that doesn't help, you may need an alignment. Check to see if it pulls when driving also. It won't pull as hard as when you stop, but if it does the alignment is off. Low tire pressure on the suspect side can cause the car to pull under braking. Possible contamination.
To the FRONT of the vehicle
The driver would need to step on the brake pedal when braking a vehicle equipped with anti-lock brakes. FYI, the driver would also need to step on the brake pedal when braking a vehicle that is NOT equipped with anti-lock brakes. Hope this helps.
If the vehicle has hubcaps remove them and see if the noise stops. Check the brakes as well, something on the wheels is rubbing.
Sounds like the wheels need re-balancing - that would cause the vehicle to 'pull' to one side during braking.
My guess would be that the vehicle has a bad power brake booster.
bad
Sounds like it might be a brake pad thickness warning sensor that gets torqued when braking enough to move away from the rotor only when braking forward. It would be worth pulling the wheels off and taking a look.
I'll give a nice simple answer here. Braking efficiency is used to describe how effective your vehicle's braking system is at reducing your vehicles speed as needed and halting it when required. I would use the term as follows - Towing a trailer that is too large for your vehicle to tow will severely compromise your vehicles braking efficiency making it very difficult and/or impossible to reduce your speed when required.
Time = Distance/Speed. However, in real life, you would need to allow for comfort stops, rest stops, stops for refuelling (the vehicle as well as yourself).
On a vehicle equipped with power brakes the answer is yes. The P/B booster works on vacuum, so if the leak were severe enough it would make the brake pedal be very hard to push. Other than that, as vacuum leak would have no effect on braking.
Assuming the vehicle stops because the brakes are applied - it would be kinetic energy transferred to heat via friction with the brake pads and brake shoes (mostly). Some would be kinetic energy transformed to heat via friction with the wheels on the road and the turning parts of the axle, transmission, etc.
Yes, it is legal to pass the postal vehicle, but only on the terms of the vehicle being on it's route (delivering mail). It would be illegal/unnecessary if the vehicle was not on route, and not doing any stops.