Phy 213 Test 3 11 pts. each March 5, 1998

1. A woman exerts a 200-N force on a 40-kg crate while pushing it across a horzontal surface. The force is directed 30° below the horizontal. The coefficient of kinetic friction between the crate and the surface is 0.30. Determine the magnitude of the kinetic friction force and the acceleration of the crate.

2. A block slides down the plane. If its acceleration is 2 m/s2, what is the kinetic coefficient of friction?

3. A car of mass m passes over a bump in a road that follows the arc of a circle of radius R as in the figure (next page). A free body diagram ought to be worth a few points. Be careful with your frame of reference. Must I mention rain, doors, bedrooms etc.?

(a) What force does the road exert on the car as the car passes the highest point of the bump if the car travels at a speed v?

(b) What is the maximum speed the car can have as it passes this point before losing contact with the road?

4. Find the maximum exit speed of a circular off ramp if its radius is 200 m and the angle of inclination of the ramp above the horizontal is 37° assuming worst conditions when there is no static friction force to hold the vehicles on the road.

5. How much work is done rolling a 60 kg barrel to the top of a ramp as indicated in the figure below ?

6. How much work is done by force F = (3 i - 5 j ) N, over the displacement r = (4 i + 6j) m ?

If the force on a 60 kg object varies with position according to the formula F = (3x2 -2x + 1) N as the object moves along the x axis:

7. Find the work done by the force as the object moves from x = 1 m to x = 5 m.

8. If the object's speed was 2 m/s at x = 1 m , how fast would it be moving at x = 5 m ?10.

9.