A truck travelling at 30 m/s has a mass of 30 000kg.?

Question

A. calculate its momentum.
B. Convert the speed of the truck to km/h.
C. A small dogs runs onto the road ahead of the truck. if the driver reacts in 0.75 s, how far does he travel before applying the brakes?
D. Compare this distance if he had been travelling at 60 km/h

Answer 1

A.momentum is velocity times mass. Here this is 30*30'000=900'000 kg*m/s

B.multiply m/s by 3.6 to get km/h, you have 30*3.6=108km/h

C.distance = velocity * time, here this is 30 * 0.75 = 22.5 meters

D.60 km/h divided by 3.6 gives you 16.67 m/s. Over 0.75s the driver would have travelled just 12.5 meters, i.e. 10 meters less. So of course it is safer to driver more slowly. But the catch is, with this reasoning you can show that it is even safer to drive at 40km/h, then 20km/h, and in the end you'll find that remaining at rest is really safe. But at the end of the day, you still want the truck to get the stuff it transports somewhere, and if possible within a reasonable amount of time... ;-)

hope this helps

Answer 2

Momentum is mass times velocity
1km = 1000m, 1 sec = 1/3600hr
Distance = velocity times time

That is all you need to know.