# College Physics

a 1200kg car coasts from rest down a driveway that is inclined 20degrees. to the horizontal and is 15m long. how fast is the car going at the end of the delivery if....
(a) friction is negligible
(book answer is 10m/s)

(b) a friction force of 3000n opposes the motion?
(book answer is 5.1 m/s)

dont know where to begin to solve these 2questions. I tried differant formulas, but nothing I tried came out to the answers in the book.
help

1. 👍
2. 👎
3. 👁
1. see this very related problem:
http://www.jiskha.com/display.cgi?id=1266960070

1. 👍
2. 👎
👤
bobpursley
2. Many if not most problems in physics are not solved by plugging directly into a single equation. It is better to prceed in logical steps using formulas you are familiar with.

In this case, the place to start is with conservation of energy. The vertical drop of the runway is
H = 15 sin 20 = 5.13
The Potential energy loss MgH equals the Kinetic Energy gain, so
MgH = (1/2) M V^2
V = sqrt(2 g H) = 100.3 m/s
(I used 9.81 m/s^2 for g)
Note that you did not need to use the mass for this one.

To do the second case, subtract friction work done
3000N*15 m = 45,000 J from the potential energy decrease, and solve for V again.

M g H - 45,000 = (1/2) M V^2
You will need to use the mass this time.

1. 👍
2. 👎
3. Two long, parallel wires separated by 30 cm each carry currents of 4.0 A in a horizontal direction.

B)Find if they are in opposite directions.

1. 👍
2. 👎

## Similar Questions

1. ### physics

A 1100 kg car coasts on a horizontal road with a speed of 19 m/s. After crossing a an unpaved, sandy stretch of road 32 m long, its speed decreases to 12 m/s. (a) Was the net force done on the car positive, negative, or zero?

2. ### Physics

An extreme skier, starting from rest, coasts down a mountain slope that makes an angle of 25.0o with the horizontal. The coefficient of kinetic friction between her skis and the snow is 0.200. She coasts down a distance of 10.4 m

3. ### physics

A car of mass 1200kg travelling @ 72 km/h is brought to rest in 4s.Find a) the average deceleration b)the average braking force

4. ### Physics

An open train car, with a mass of 2150 kg, coasts along a horizontal track at the speed 2.29 m/s. The car passes under a loading chute and, as it does so, gravel falls vertically into it for 2.67 s at the rate of 441 kg/s. What is

1. ### PHYSICS HELPPPP

A loaded ore car has a mass of 880 kg and rolls on rails with negligible friction. It starts from rest and is pulled up a mine shaft by a cable connected to a winch. The shaft is inclined at 28.0° above the horizontal. The car

2. ### PHYSICS

A car is traveling up a hill that is inclined at an angle θ above the horizontal. Determine the ratio of the magnitude of the normal force to the weight of the car when (a) θ = 15o and (b) θ = 32o.

3. ### physics

A 2100 car starts from rest at the top of a 5.0m long driveway that is sloped at 20 degrees with the horizontal. If an average friction force of 4000N impedes the motion find the speed of the car at the bottom of the driveway.

4. ### physics

an extreme skier starting from rest, coasts down a mountain that makes an angle 25.0¨¬with the horizontal. The coeffiecient of kinetic friction between her skis and the snow is 0.200. She coasts for a distance of 8.4m before

1. ### Physics

Amechanic pushes a 2.50*10^3 kg car from rest to a speed of v, doing 5.00*10^3 Jof work in the process, During this time, the car moves 25.0m. Neglecting friction between car and road, find (a) v and (b) the horizontal force

2. ### physics-energy

HI well i have two questions 1) a 2.0-m-long pendulum is released from rest when the support string is at an angle of 25 with the vertical. what is the speed of the bob at the bottom of the swing? 2)A 2.0*10^3-kg car starts from

3. ### physics

A car of mass 1200kg travelling at 72km/h was brought to rest in 4 seconds. 1. what is this period in m/s? 2. find; a. the deceleration of the car. b. the force that caused the car to come to rest. c.the distance it travelled

4. ### Physics

A 4.0 × 103 kg car accelerates from rest at the top of a driveway that is sloped at an angle of 19.6◦ with the horizontal. An average frictional force of 4.0×103 N impedes the car’s motion so that the car’s speed at the