Work & Energy Q&A: Get Answers & Verification Here

[joejo]

Hi,
I have placed my answer below the question. I'm having doubts that it is right! Can someone please help me verify it. Thanks in advance!

1. State the SI units to measure:
a. Work. joules
b. Kinetic Energy. joules
c. Power. watts

2. Calculate the work done by a 140kg black bear that climbs 18m up a tree. 24696J

3. A golf ball is given 115 J of energy by a club that exerts a force over a distance of 4.5cm while the club and the ball are in contact.
a. Calculate the magnitude of the average force exerted by the club on the ball.
b. If the ball’s mass is 47g, find the magnitude of its average acceleration.
c. What speed does the club impart to the ball? for 3...i got 2555.56N

4. A 55kg diver has 1.62 kJ of gravitational potential energy relative to the water when standing on the edge of a diving board. How high is the board above the water? 3.01m

5. Calculate the power of a light bulb that transforms 1.5x104 J of energy per minute. 250w

6. A chair lift takes skiers to the top of a mountain that is 320 m high. The average mass of a skier complete with equipment is 85 kg. The chair lift can deliver three skiers to the top of the mountain every 35s.
a.Determine the power required to carry out this task. (Assume the skiers join the lift at full speed.)
b.If friction increases the power required by 25%, what power must the motors running the lift be able to deliver?

for 6...
Eg=mgh
=85kg*9.8N/kg*320m
=266560J 2.7*10 to the 5

or

Ek= 1/2mvsquared
= ½(85kg) (9.1m/s)
=3519.43J

for 6.b)

im thinking...
=53312J

dont understand how to do 6 and 3 and also, if they rest are right?!

Thanks in advance for your help!

 

[ek]

Q6 is asking for the power, not energy.

P = mgh/t

And for Q6b, I'd assume the answer is just 5mgh/4t.

Edit: And remember there are three skiers at 85kg each, not just one.

 

[thepatientmental]

Hi there! I'll try to help you verify your answers and also provide some explanation for the questions you're unsure about.

1. Your answers for the SI units are correct! Good job.

2. Your calculation for the work done by the black bear is also correct. You can double check it by using the formula W = mgh, where m is the mass (140kg), g is the acceleration due to gravity (9.8 m/s^2), and h is the height (18m). So, W = (140kg)(9.8 m/s^2)(18m) = 24696J.

3. a. To calculate the average force exerted by the club on the ball, we can use the formula W = Fd, where W is the work done (115J), d is the distance (4.5cm = 0.045m), and F is the force we are trying to find. So, F = W/d = (115J)/(0.045m) = 2555.56N. Your answer is correct!

b. To find the magnitude of the average acceleration, we can use the formula F = ma, where F is the force we just calculated (2555.56N), m is the mass (47g = 0.047kg), and a is the acceleration we are trying to find. So, a = F/m = (2555.56N)/(0.047kg) = 54475.32 m/s^2. However, this seems like a very high acceleration for a golf ball, so it's possible that there is an error in the question or in your calculation.

c. To find the speed imparted to the ball by the club, we can use the formula Ek = 1/2mv^2, where Ek is the kinetic energy (115J), m is the mass (47g = 0.047kg), and v is the speed we are trying to find. So, v = √(2Ek/m) = √[(2)(115J)/(0.047kg)] = 62.75 m/s. Again, this seems like a very high speed for a golf ball, so it's possible that there is an error in the question or in your calculation.

4. Your calculation for the height of the diving board is correct. You can also use the formula PE = mgh, where PE