A mass m 1 = 4.9 kg rests on a frictionless table and connected by a massless st

Question

A mass m1 = 4.9 kg rests on a frictionless table and connected by a massless string over a massless pulley to another mass m2 = 4.6 kg which hangs freely from the string. When released, the hanging mass falls a distance d = 0.79 m.

1)

How much work is done by gravity on the two block system?

J

2)

How much work is done by the normal force on m1?

J

3)

What is the final speed of the two blocks?

m/s

4)

How much work is done by tension on m1?

J

5)

What is the tension in the string as the block falls?

N

6)

The work done by tension on only m2 is:

positive

zero

negative

7)

What is the NET work done on m2?

J

Explanation / Answer

1) Wg = m2*g*h = 4.6*9.81*0.79 = 35.64 J

2) Wn = N*S*cos(90) = 0 J

3) Tension is T then

T = m1*a

m2g-T = m2*a

m2g-m1a = m2*a

accelaration a = m2*g/(m1+m2) = 4.6*9.81/(4.9+4.6) = 4.75 m/s^2

using v^2 - u^2 = 2*a*S

v^2 = 2*4.75*0.79

v = 2.74 m/s

4) W = 0.5*m1*v^2 = 0.5*4.9*2.74^2 = 18.4 J

5) T = m1*a = 4.9*4.75 = 23.275 N

6) Negative

7) W = (m2a*S =(4.6*4.75)*0.79 = 17.26 J

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