Help Needed: Solving Two Tough Physics Problems

[jkd989]

A bodybuilder is holding a 35-kg steel barbell above her head. How much force would she have to exert if the barbell were lifted underwater?

In the hydraulic press used in a trash compactor, the radii of the input piston and the output plunger are 6.1 10-3 m and 4.5 10-2, respectively. If the height difference between the input piston and the output plunger can be neglected, what force is applied to the trash when the input force is 300 N?

Please answer these questions for me, they are the last two problems on my 100 problem worksheet that is due tomorrow. I have literally spent the past two hours trying to find the answers for these and i really need a good grade...Thanks in advance!

 

[russ_watters]

We don't just give answers here. Tell us how you have started these problems. (hint: do you understand the concepts of buoyancy and levers?)

[multi-post...locking]

 

[quicknote]

I am happy to help you with these two physics problems. Let's start with the first one about the bodybuilder and the steel barbell. In order to solve this problem, we need to first understand the concept of buoyancy. When an object is submerged in water, it experiences an upward force called buoyant force, which is equal to the weight of the water displaced by the object. This means that the buoyant force on the barbell will be equal to the weight of the water it displaces.

To calculate the weight of the water displaced, we need to know the volume of the barbell. Let's assume the barbell has a density of 7.8 g/cm3, which is the density of steel. This means that the volume of the barbell will be 35 kg / 7.8 g/cm3 = 0.00449 m3. Now, we can use the formula for the weight of water, which is density x volume x gravity (ρVg), to calculate the weight of the water displaced by the barbell. This comes out to be 0.00449 m3 x 1000 kg/m3 x 9.8 m/s2 = 43.9 N.

Since the buoyant force is equal to the weight of the water displaced, the bodybuilder would have to exert a force of 43.9 N in order to lift the barbell underwater.

Moving on to the second problem about the hydraulic press, we can use the principle of Pascal's law to solve it. According to this law, pressure applied to a fluid in a closed container is transmitted equally to all parts of the fluid and the walls of the container. This means that the pressure applied on the input piston will be transmitted to the output plunger, causing it to exert a force on the trash.

To calculate the force applied on the trash, we can use the formula for pressure, which is force/area (P = F/A). Since the area of the input piston is given as 6.1 x 10-3 m2 and the force applied on it is 300 N, the pressure applied on the input piston would be 300 N / 6.1 x 10-3 m2 = 49,180 Pa.

Now, since the pressure is transmitted equally to all parts of the fluid, we can use the same pressure value to calculate the force applied on the output pl