4.A 31-cm long conducting wire of 9-g carrying 7- A current is placed in a uniform magnetic field. What are the strength and dir
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Answer:
Approximately , assuming that
.
Explanation:
Let and
denote the mass and acceleration of Spiderman, respectively.
There are two forces on Spiderman:
- Downward gravitational attraction from the earth:
.
- Upward tension force from the strand of web
.
The directions of these two forces are exactly opposite of one another. Besides, because Spiderman is accelerating upwards, the magnitude of (which points upwards) should be greater than that of
(which points downwards towards the ground.)
Subtract the smaller force from the larger one to find the net force on Spiderman:
.
On the other hand, apply Newton's Second Law of motion to find the value of the net force on Spiderman:
.
Combine these two equations to get:
.
Therefore:
.
By Newton's Third Law of motion, Spiderman would exert a force of the same size on the strand of web. Hence, the size of the force in the strand of the web should be approximately (downwards.)