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

• joejo
In summary, questions were asked about SI units for measuring work, kinetic energy, and power. Calculations were done for the work done by a black bear climbing a tree, a golf ball being hit by a club, and a diver standing on a diving board. The power of a light bulb and a chair lift carrying skiers up a mountain were also calculated. The conversation also mentioned doubts about some answers and confusion about how to approach certain problems.
joejo
Hi,

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?!

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.

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

## 1. What is work?

Work is a measure of the amount of energy transferred by a force acting through a distance.

## 2. How is work calculated?

Work is calculated by multiplying the force applied in the direction of motion by the distance the object moves.

## 3. What is the unit of work?

The unit of work is joule (J) in the International System of Units (SI).

## 4. What is energy?

Energy is the ability to do work or cause change.

## 5. What are the different forms of energy?

The different forms of energy include kinetic energy, potential energy, thermal energy, chemical energy, electrical energy, and nuclear energy.

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