Physics + Logic = tired brain :biggrin:

  • #1
This one should be quick and easy, but I just can't seem to get it:

"A college rower can easily push a small car along a flat road, but she cannot lift the car in the air. Since the mass of the car is constant, how can you explain this discrepancy?"

Edit: I'm thinking that friction can be overcome more easily than gravity...but I'm struggling to prove that.
 
Last edited:

Answers and Replies

  • #2
161
0
Think about the forces that are acting. What is the difference in direction between lifting it up, and pushing it across?
What are the forces acting in these directions?
 
  • #3
161
0
Sorry, just read your edit...... remember friction force is given by mu * N
(normal force). Where mu is the co-efficient of friction - you might be able to estimate this, or find an approximate value somewhere.
The force acting due to gravity is F=mg.
I hope this gives you enough to go on with........
 
  • #4
tyco05 said:
Sorry, just read your edit...... remember friction force is given by mu * N
(normal force). Where mu is the co-efficient of friction - you might be able to estimate this, or find an approximate value somewhere.
The force acting due to gravity is F=mg.
I hope this gives you enough to go on with........
Yes, thank you!! :biggrin:
 
  • #5
PPonte
The force to lift the car up is [itex]F = m.g[/itex].
The force to push the car along a flat road is [itex]F > \mu_s.m.g[/itex]

Compare this two forces.

HINT: Between what values is usually [itex]\mu_s[/itex].
 
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