# Re: PHYSICS

"Relative" is an important word. Block L of mass mL = 1.90 kg and block R of mass mR = 0.500 kg are held in place with a compressed spring between them. When the blocks are released, the spring sends them sliding across a frictionless floor. (The spring has negligible mass and falls to the floor after the blocks leave it.)
(a) If the spring gives block L a release speed of 1.80 m/s relative to the floor, how far does block R travel in the next 0.800 s?
(b) If, instead, the spring gives block L a release speed of 1.80 m/s relative to the velocity that the spring gives block R, how far does block R travel in the next 0.800 s?

* Physics - bobpursley, Sunday, February 25, 2007 at 5:22pm

Momentum L has is equal to the momentum R has.

1.90*1.80=.500*veloictyR

Relative to each other, velocityLrelative=VelocityRrelative

Now to compute the distance here, obviously the relative distances are of no value....they equal each other. Here you have to convert to an absolute relative to floor velocity. AGain, use the principle that the center of gravity is constant, or, the momentums are equal.

* Physics - COFFEE, Sunday, February 25, 2007 at 11:47pm

1.9*1.8=.5*velocityR
velocityR = 6.84 m/s

d=v*time
d=(6.84)(.8)
d=5.472m

* Re: PHYSICS - bobpursley, Tuesday, February 27, 2007 at 7:17am

yOu need to use average velocity, not initial velocity. The average velocity is 1/2 the initial velocity.

distance=averagevelocity*time

So I did...

d=(-1.8+6.84)(.8)
d=2.016m

This is wrong. What am I doing wrong?

"Relative" is an important word. Block L of mass mL = 1.90 kg and block R of mass mR = 0.500 kg are held in place with a compressed spring between them. When the blocks are released, the spring sends them sliding across a frictionless floor. (The spring has negligible mass and falls to the floor after the blocks leave it.)
(a) If the spring gives block L a release speed of 1.80 m/s relative to the floor, how far does block R travel in the next 0.800 s?
(b) If, instead, the spring gives block L a release speed of 1.80 m/s relative to the velocity that the spring gives block R, how far does block R travel in the next 0.800 s?

"Relative" is an important word. Block L of mass mL = 1.90 kg and block R of mass mR = 0.500 kg are held in place with a compressed spring between them. When the blocks are released, the spring sends them sliding across a frictionless floor. (The spring has negligible mass and falls to the floor after the blocks leave it.)
(a) If the spring gives block L a release speed of 1.80 m/s relative to the floor, how far does block R travel in the next 0.800 s?
****Momentum is conserved: mL*vL=mR*Vr implies that
Vr=mL/mR *vL= 1.90/.500 (1.80) = 6.84 m/s
distanceR=6.84*.800=5.47 meters with respect to the floor.
(b) If, instead, the spring gives block L a release speed of 1.80 m/s relative to the velocity that the spring gives block R, how far does block R travel in the next 0.800 s?
****Momentum is conserved: mL*vL=mR*Vr implies that
Vr=mL/mR *vL= 1.90/.500 (1.80) = 6.84 m/s with respect to the velocity given L

At this point, consider the words "relative to the velocity that the spring gives block R." That means to me, L is moving at 1.84 less than R is moving to the right. If R is fixed, then L is moving 1.84 to the left. If R is moving 10m/s to the right, then L is moving 10-1.84 to the RIGHT.
Here, vL=vR-1.84 where vL, vR are relative to floor.
and vR= 6.84-vL where vL,vR are relative to floor.
So vR= 6.84-vL = 6.84-vR+1.84
vR= 4.34 m/s
check my thinking and math.

1. 👍 0
2. 👎 0
3. 👁 967

## Similar Questions

1. ### Physics

Block 1, of mass m1 = 0.650kg , is connected over an ideal (massless and frictionless) pulley to block 2, of mass m2, as shown. For an angle of θ = 30.0∘ and a coefficient of kinetic friction between block 2 and the plane of μ

2. ### Physics

A block of mass m = 2.00 kg rests on the left edge of a block of mass M = 8.00 kg. The coefficient of kinetic friction between the two blocks is 0.300, and the surface on which the 8.00- kg block rests is frictionless. A constant

3. ### physics

A block of mass m = 3.53 kg is attached to a spring which is resting on a horizontal frictionless table. The block is pushed into the spring, compressing it by 5.00 m, and is then released from rest. The spring begins to push the

4. ### Physics

A block of mass 3m is placed on a frictionless horizontal surface, and a second block of mass m is placed on top of the first block. The surfaces of the blocks are rough. A constant force of magnitude F is applied to the first

1. ### physics

In the Figure the pulley has negligible mass, and both it and the inclined plane are frictionless. Block A has a mass of 1.3 kg, block B has a mass of 2.7 kg, and angle è is 26 °. If the blocks are released from rest with the

2. ### cary collage

"A 2.5-kg block slides down a 25 degree inclined plane with constant acceleration. The block starts from rest at the top. At the bottom, its velocity reaches 0.65 m/s. The length of the incline is 1.6m. a) What is the acceleration

3. ### Physics

Block A sits on a horizontal tabletop. There is friction between the surface and Block A. The string passes over a frictionless, massless pulley. Block B hangs down vertically. When the two blocks are released, Block B accelerates

4. ### physics

A 3 kg block (block A) is released from rest at the top of a 20 m long frictionless ramp that is 5 m high. At the same time, an identical block (block B) is released next to the ramp so that it drops straight down the same 5 m.

1. ### Physics

A block of mass M rests on a block of mass M1 = 5.00 kg which is on a tabletop. A light string passes over a frictionless peg and connects the blocks. The coefficient of kinetic friction mk at both surfaces equals 0.330. A force

2. ### physics

A heavy wooden block rests on a flat table and a high-speed bullet is fired horizontally into the block, the bullet stopping in it. How far will the block slide before coming to a stop? The mass of the bullet is 10.5 g, the mass

3. ### physics

a block of mass 3 kg rests on a smooth table and connected to another block of mass 2 kg, after passing over and ideal pulley, the block of mass 2 kg is released. how long does it take the block to travel 80 cm

4. ### physics

A block of mass M rests on a block of mass M1 = 5.00 kg which is on a tabletop. A light string passes over a frictionless peg and connects the blocks. The coefficient of kinetic friction mk at both surfaces equals 0.330. A force