1.
You lower a 42.40-kg box to the floor from a shelf 0.80m above the floor. If you lower the box
with a constant speed, what is the force you exert on the box? Is it upward or downward? (You
must answer both parts to get credit.) (in N)
Solution
Let's assume that the person is standing on the floor and his/her height is greater than or equal to
0.80m.
Since the movement is happening with constant speed, there is no acceleration, as acceleration is
the rate of change of speed.
Thus, to lower the box smoothly on the ground and to prevent it from a free fall, the person must
apply a force equal to the weight of the box.
As per given data, weight of the box = mg= 42.40 kg * 9.8 ms -2
[ as g = acceleration due to
gravity = 9.8 ms -2
]
Or, weight of the box = 415.52 N
Since the weight of the box acts downwards, the force applied must be upwards.
Thus, the force exerted on the box is 415.52 N, acting upwards .