(a) When attempting to stop a car quickly on dry pavement, which of the followin

Question

(a) When attempting to stop a car quickly on dry pavement, which of the following methods will stop the car in the least time? ? (i) Slam on the brakes as hard as possible, locking the wheels and skidding to a stop. (ii) Press the brakes as hard as possible without locking the wheels and rolling to a stop. Explain. (b) A stone hangs by a fine thread from the ceiling, and a section of the same thread dangles from the bottom of the stone (as shown). If a person gives a sharp pull on the dangling thread, where is the thread likely to break: below the stone or above it? What if the person give a slow and steady pull? Explain your answers.

Explanation / Answer

press the brakes as hard as possible without locking the wheels and rolling to a stop

when wheels are not locked and rolling, the firctional force acting is greater as compared to the case when wheels are locked and skidding. so larger frictional force in case of rolling without locking the wheels makes the car to stop in the least time.

b)

the upper thread connected to stone does not experience the force exerted at the dangling thread since the stone resist any change in its state of rest. hence all the force is on the lower end and it breaks.

when the person slowly pulls , the force is transfered to the upper thread and hence the upper thread breaks

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