Thread: Mechanics question

Originally Posted by nazz

A man of mass 80kg is in a balloon basket of mass 40kg. The man is holding a bag of ballast of mass 60kg.
the basket with its contents attached to a balloon are accelerating downwards at 2.8m/sec^2
a) what is the force exerted by the man on the bag of ballast?
b) what forces are exerted on the man by
i) the bag of ballast? equal and opposite to the force exerted by the man on the ballast (3rd law, right?)
ii) the basket? basket pushes up on the man ... what other force acts on the man? ... net force on the man?

Ans
a) 60g- R = 60x2.8 ( where R is the force exerted by the man on the bag)
R= 420N
b)
i) 60g= 588N ( force exerted by the bag on the man)
ii) (420+ 80g) - B = 80x2.8 ( where B is the force of the basket on the man)

question , is part I and ii correct not sure

...

What about calculations for part i and ii ? Are they correct?

forces on the ballast ...

60g - R = 60a

R = 60(g-a) = 420 N


forces on the man ...

80g + R - B = 80a

80(g - a) + R = B

Shouldn't R be negative as it is upwards so the equation should be 80g -R-B=80a

man's force on the bag is upward

bag's force on the man is equal, but in the opposite direction by Newton's 3rd law ... downward

Makes sense so the force on the man are force of the bag on man, his weight and what about the weight of the bag on the man?

60g - R = 60a

R acts on the man ... the weight of the bag contributes to the magnitude of R as shown in the equation

Many thanks for the feedback