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Reaction time and stopping distance

0 votes
A pedestrian was stuck and seriously injured by a truck which left skid marks 28.5m long. Prior to skidding, the truck was travelling at 72km/hr^-1.

 

1. Determine the speed of the truck in metres per second (m/s^-1) prior to skidding.

 

2. If the truck driver took 0.75s to react, estimate the stopping distance in metres of the truck.
asked Aug 20, 2013 in PHYSICS by JacobB Rookie

2 Answers

0 votes

1.

Use conversion factors to convert speed from km/hr to m/s

1km = 1000m
1 hour = 60 minutes = 3600 seconds

Speed of the truck prior to skidding = 72 km / hr

                                                                = 72 (1000 m) / (3600 s)

                                                                = 72000 m / 3600 s

                                                                = 20 m/s

Speed of the truck im meters per second prior to skidding is 20 m/s

 

answered Aug 20, 2013 by Naren Answers Apprentice
0 votes

2.


stopping distance = skidding distance + reacting distance


                          = 28.5 m+ speed of the truck prior to skidding x reaction time

                          = 28.5 m + 20m/s x 0.75s

stopping distance = 28.5m + 20 m = 43.5m

answered Aug 22, 2013 by Naren Answers Apprentice

Stopping distance = skidding distance + reacting distance


                           = 28.5 m+ speed of the truck prior to skidding x reaction time

                           = 28.5 m + (20m/s x 0.75s)

Stopping distance = 28.5m + 15m = 43.5m.

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