Saturday

January 24, 2015

January 24, 2015

Posted by **Agata** on Tuesday, November 15, 2011 at 8:57pm.

- physics -
**drwls**, Tuesday, November 15, 2011 at 9:11pmThe amount of work that a car must do to slow down is proportional to the kinetic energy (KE) change.

The entity that the car is pushing against to slow it down is actually doing negative work, of the same magnitude.

The ratio of the KE changes is

[(20)^2 - (10)^2]/10^2

= 300/100 = 3

The deceleration from 20 to 10 kph requires that 3 times as much work be done by the car.

Note that I did not have to compute the KE or change speed units to m/s to get this result. Only the ratio is important for this problem.

**Answer this Question**

**Related Questions**

physics - is the work needed to bring a car's speed from 0 to 10 km/h less than...

Physical Science - is the work needed to bring a car's speed from 0 to 10 km/h ...

physical sciencei - is the work needed to bring a car's speed from 0 to 10 km/h ...

Physics - A car with a mass of 1500 kg moves at 26 m/s. What braking force is ...

physics - A car with a mass of 1435 kg moves at 11 m/s. What braking force is ...

physics - A force of -9000 N is used to stop a 1500kg car traveling at 20 m/s. ...

Physics - How many joules of energy per kilogram of rest mass are needed to ...

Physics - In black-and-white photography, a photon energy of about 4.00 x 10-19...

physics - a mass (m=2.00kg) is traveling at an initial speed of 18.0m/s. find ...

Physics - A speed trap is set up with two pressure-activated strips placed ...