A car driver is travelling at speed v on a straight road. He comes over the top of a hill to find a fallen tree on the road ahead. He immediately brakes hard but travels a distance of 60 m at speed v before the brakes are applied. The skid marks left on the road by the wheels of the car are of length 140 m, as shown.

The police investigate whether the driver was speeding and establish that the car decelerates at 2.0 m s⁻² during the skid.

a. Determine the initial speed v of the car before the brakes are applied.

b. Determine the time taken between the driver coming over the top of the hill and applying the brakes. Suggest whether this shows whether the driver was alert to the danger.

c. The speed limit on the road is 100 km/h. Determine whether the driver was breaking the speed limit.

Transcribed Image Text:

top of hill skid marks 60 m 140 m Figure 2.39