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Ex 2) A 10 kg frictionless cart is resting on a horizontal table. A force of 10 N is applied to the cart for a distance of 8 m. What is the carts new kinetic energy?
m = 10 kg F = 10 N d = 8 m KE = (˝)mv2 ??
ΔKE = W
= Fd = 10N(8m)
= 80 Nm
Ex 3) 100 Joules of work is needed to lift a 100 kg object from the ground.
W = ΔPE = 100J
Ex 4) Crate is pulled 6.00 m up an incline with a force of 50.0 N. If the PE of the cart increases by 250. J. , what is the total work done against friction?
d = 6.00 m F = 50.0 N ΔPE = 250. J
W = Fd = 50.0 N(6 m)
= 300. J
W = ΔPE + Wf 300. J = 250. J + Wf Wf = 50.0 J
KE = (1/2)mv2
Work on object = ΔKE ΔKE = W = Fd = 4 N(2 m)
= 8 Nm
B. Find the objects velocity
KE = (1/2)mv2
8 Nm = (1/2)1 kg(v2)
16 = v2
V = 4 m/s
Ex 6) A force of 100.0 N lifts the object 10.00 m off the ground. What is the object's new potential energy?
ΔPE = W = Fd = 100.0 N(10.00 m)
= 1000. Nm
What is the mass of the object?
= m(9.8 m/s2)10.00 m = 1000. J
m = 10.20 kg
Ex 7) A spring has a spring constant of 2.0 N/m. How much work must be done to stretch it 5.0 m from its equilibrium position?
W = PE = 1/2kx2
= (1/2)2.0 N/m(5.0 m)2
= 25. J
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