physics problems (3)

Question

1. a 5 -newton force cause a spring to strech 0.2m. what is the potential energy stored in the stretch spring?

2.a student does 60 J of work pushing a 3kg box up the full length of a ramp that is 5m long. what is the magnitude of the force applied to the box to do this work?

3.during a s interval, the velocity of an object changes from 25m/s east to 15m/s east.determine the magnitude and direction of the acceleration of the object.

explain in details

Answer 1

1.
F = 5 N, Δx = 0.2 m

Potential energy stored in the stretched spring P.E.
= F•Δx
= 5 x 0.2
= 1 J

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2.
W = 60 J, s = 5 m

W = F•s

Force applied to the box F
= W / s
= 60 / 5
= 12 N

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3.
Direction to the east = +ve
Direction to the west = -ve

u = +25 m/s, v = +15 m/s, t = 1 s
v = u + at

Acceleration a
= (v - u) / t
= (15 - 25) / 1
= -10 m/s2

Magnitude of acceleration = 10 m/s2
Direction of acceleration : pointing to the west