2. An unstretched spring is 10 cm. long. A force of 10N compresses it to 9 cm. a

ID: 1293679 • Letter: 2

Question

2. An unstretched spring is 10 cm. long. A force of 10N compresses it to 9 cm.

a. How much force is needed to stretch it to 12cm.?

b.How much energy is needed to stretch it from 10cm. to 12cm.?

3. The box below has a mass of 120kg. It is 50 cm. from pivot A.

From pivot A to pivot B is 2 meters. The plank has no mass.

a. What is the force on point A?

b. What is the force on point B?

4. A 2kg ball moving 3m/s has an elastic collision with a brick wall.

a. What is its change in momentum?

b. What impulse did it receive from the wall?

5. A 4kg ball is moving to the right at a velocity of 3m/s. An 8kg ball

is moving to the left with a velocity of -3m/s. The 4kg ball bounces

off the 8kg ball and the 4kg ball is now moving -2m/s to the left.

a. How fast is the 8 kg ball moving after the collision?

b. Was this an elastic collision?

6. A 60kg student walked up 40 meters of stairs.

a. How much work did he do?

b. Assume 25% efficiency. How much energy did it take?

c. How many calories (cal) did it take?

d. How many Calories (Cal) did it take?

F=-kx

we are given

F=10 N and x=10-9=1 cm=0.01 m

putting in formula we can find k, force constant

a) in this part

x=12-10=2 cm=0.02 m

we know k

putting in F=-kx

we can find F

energy E=F.d

d=0.02 m

we can find E

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