W1 = 2kg connected to W2 = 1kg over pulley.
net F = 9.8 N on system; a = F/m = 9.8N/3kg = 3.3 m/s2.
- In the above drawing when the weights are released the acceleration of
weight 1 will be
- A. 4.9 m/s2 downwards.
- B. 3.3 m/s2 downwards.
- C. 2.45 m/s2 downwards.
- D. 1.23 m/s2 downwards.
- E. 9.8 m/s2 downwards.
- Dobbin, Farmer Brown's horse, refuses to be hitched to the wagon to
pull it into town, claiming "Newton's third law states that if I pull on
the wagon, the wagon pulls back equally hard on me, so it is futile to try
to pull the wagon." What is wrong with Dobbin's argument?
- A. Nothing, Dobbin's argument is correct.
- B. Dobbin is incorrect that the wagon pulls back on him as hard as he
pulls on the wagon; he pulls slightly harder forward than the wagon pulls
backward.
- C. Dobbin is mostly correct, but as he starts up he
instantaneously pulls harder on the wagon, after that he need merely
pull at the same strength to keep the wagon in motion.
- D. Dobbin can only pull the wagon forward if he weighs more than the wagon.
- E. Dobbin is partially correct, but his argument is irrelevant; the
forward force of the ground (friction) on Dobbin exceeds the backward pull
of the wagon so Dobbin moves forward and the wagon follows along.
Spring 2004
