# Science check

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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?

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?

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

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.