An 8.0 kg block is released from rest, v1 = 0 m/s, on a roughincline, which has an angle of 40 from the horizontal. The blockmoves a distance of 1.6 m down the incline, in a time interval of0.80 s, and acquires a velocity of v2 = 4.0 m/s.

The average rate at which friction force does work during the 0.80s time interval is closest to:

a. +40 W
-b. + 20 W
-c. 0-
-d. â40 W
-e. â20 W

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Lelia LubowitzLv2

13 Jun 2019

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1. A block is placed on a plane whose angle of inclination is 30˚. The coefficients of static and kinetic friction for the block on the inclined plane are both 0.2. The block
(A) remains stationary on the inclined plane.
(B) accelerates down the inclined plane.
(C) travels down the inclined plane at a constant velocity.
(D) travels up the inclined plane at a constant velocity.
(E) accelerates up the inclined plane.

2. An object with a mass of 5.5 kg is allowed to slide from rest down an inclined plane. The plane makes an angle of 30˚ with the horizontal and is 72 m long. The coefficient of friction between the plane and the object is 0.35. The speed of the object at the bottom of the plane is?

3. A 5-kg object slides down a frictionless surface inclined at an angle of 30˚ from the horizontal. The total distance moved by the object along the plane is 10 meters. The work done on the object by the normal force of the surface is?

4. A mass m = 2.5 kg is sliding along a frictionless table with initial speed v as shown in the figure. It strikes a coiled spring that has a force constant k = 500 N/m and
compresses it a distance x=5.0 cm. The initial speed v of the block was..?

5. The graph shows how the position of a particle depends on time. Which choice is closest to the instantaneous speed of the particle at t = 3s?
(A) 0.40 m/s
(B) 0.67 m/s
(C) 0.75 m/s
(D) 1.50 m/s
(E) 2.22 m/s

6. Calculate the work done by a force, F = 2x i, along the
path (0, 0) -> P₁(2, 0) -> P2(2, 2).

turquoisearmadillo973

Consider the following system ashaving frictionless surfaces. A 20 kg block is connected by astring to a 30 kg block over a frictionless pulley. The 30 kg blockis also connected to a spring, which is currently at equilibrium 20cm above a table top. The 20 kg block, originally at a height of 45cm above the table top, is pulled down the incline a distance of 20cm - stretching the spring and raising the 30 kg mass to a heightof 40 cm (20 cm above its original position). The 20 kg block isthen released from rest.

If k=250 N/m, find the velocity of the 30 kg mass as it reachesits original height on its way back down.

[hint: Use conservation of energy, setting U = 0 at theequilibrium point of the spring. Also note that the 45 cm height ofthe 20 kg block is not its initial height.]

Please help with these questions !!
1. A rope is towing a 100 kg rock, from rest, with a force of 10 Nthat varies with time. At the end of 8.0 sec, the velocity of therock is?
Answer is: zero

2. A 3 kg mass is positioned at (0,8) and a 1 kg mass is postionedat (12,0). What are the coordinates of a 4 kg mass which willresult in the center of the mass of the system of three massesbeing located at the origin (0,0)?
The answer is (-3,-6)

3. A car traveling 20 m/s rounds an 80 m radius horizontal curvewith the tires on the verge of slipping. How fast can this carround a second curve of radius 320 m? (assume the same coefficientof friction between the car's tires and each road surface).
The answer is: 40 m/s

Thanks !!

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