Posted by **Anonymous** on Tuesday, May 29, 2007 at 4:40pm.

I was wondering if someone could check the problems for me? Thanks I can go back and show work if needed..this was just easier to type out.

1)An object has a mass of 615 grams and a volume of 105cm3.What is the density of the object?

answer 5.86 gm/cm3

2) A player uses a hockey stick to increase the speed of a 0.200 kg hockey puck by 6 m/s in 2 seconds.?

a) how much did the hockey puck accelerate?

answer-3 m/s2

b) how much force was exerted on the puck?

answer .6N

c) how much force did the puck exert on the hockey stick?

answer -.6 N

3) Find the net force produced by a 40 newton force and a 50 newton in each case

A)both forces act in the same direction

B)bother forces act in opposite directions

I am not sure :-/

4)A car of mass 900kg moves at 10 m/s. What is the breaking force required to stop the car in 5 seconds

Not sure either

5)A 10 kg go-cart is moving at a speed of 3 m/s. what is the kinetic energy?

45J

6) if an engine must do 500 joules of work to pull a 10 kg load up to a height of 4 meters, what is the efficiency of the engine?

80%

Thanks

oh two more I forgot sorry

1)Suppose you want to heat 40 kg of water by 20c how many joules of heat are required?

3344 J

2)How many joules of heat are required to melt 40kg of ice at 0 degrees C?

13360 J, akk I am thinking that is off

The density is ok but g is grams and not gm.

On supolementary 1, I think you forgot to multiply 40 kg by 1000 to change to grams.

40 kg x 1000 g/kg x 4.184 J/g*C x 20 degrees C = ??

2. 40 kg x 1000 g/kg x heat of fusion = ??

You lost me...

1)Suppose you want to heat 40 kg of water by 20c how many joules of heat are required?

3344 J

**40,000 g x 4.184 J/g*C x 20 C = joules heat required to heat 40 kg water by 20 degrees C.**
2)How many joules of heat are required to melt 40kg of ice at 0 degrees C?

13360 J, akk I am thinking that is off

J = 40,000 g x heat of fusion ice = 40,000 g x 334 J/g = ??

Look up the heat of fusion of water. I may not have remembered 334 J/g correctly but I think that is right.

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