Answer:
39.2m/s
Explanation:
The potential energy the book has right before it falls is equal to the kinetic energy in falling.
PE = KE
mgh = (1/2)mv
2gh=v
v=(2)(9.81)(2)
v=39.24m/s
The elastic potential energy of the spring is 0.31 J
Explanation:
The elastic potential energy of a spring is given by

where
k is the spring constant
x is the compression/stretching of the spring
For the spring in this problem, we have:
k = 500 N/m (spring constant)
x = 0.035 m (compression)
Substituting, we find the elastic potential energy:

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Explanation:
The magnetic needle of a compass lines up with Earth's magnetic poles.
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Answer:
Al's mass is 102.92 kg
Explanation:
As there are no external forces in the horizontal direction, the horizontal net force must be zero:
As the force is the derivative in time of the momentum, this means that the horizontal momentum is constant:

where the suffix i and f means initial and final respectively.
The initial momentum will be:

But, as they are at rest, initially


So, this means:

We know that the have an combined mass of 195 kg:
.
so:
.





Now, we can use the values:


where the minus sign appears as they are moving at opposite directions


and this is the Al's mass.