Question

A running back holds 0.25 kg football and runs 100m down the football field. In addition to scoring six points for his team, he also does ___ work on the football

A) no
B) 25 J of
C) 100 J of
D) 250 J of

Select the option which will cause a worker to do the maximum amount of work.
A) Using a lever to lift 100 newtons up to 4 meters on to a shelf
B) Using her hands to lift 200 newtons up 1 meter on to a table
C)Using a ramp to lift a 200 newton box up 1 meter into a truck
D) Using a pulley to lift to 100 newton box up 3 meters onto a platform

The power resulting from 420 Nm of work being completes in 3 seconds
A) 140 Joules
B)140 Newton-meters

What do you know about the law of conservation of energy? Check all the statements that are true

A)The total amount of mass in a system remains constant regardless of the changes that take place in system
B) Energy is neither creates or destroyed, it only changes form
C) Half-way down the ramp, PE = 50J and KE = 50J
D) In a closed system, a system that isolated from its surrounds, the total energy of the system is conserved

Answer 1

1) there is no work done on the system

2) A) Using a lever to lift 100 newtons up to 4 meters on to a shelf

3) P = 140 W

4) D) In a closed system, a system that isolated from its surrounds, the total energy of the system is conserved

Step-by-step explanation:

1) As we know that work done is the product of force and the displacement of the point of action where force is applied

So here we have

`W = 0`

as there is no displacement in the direction where the force is applied

2)As we know that work is product of force and displacement

So we will have

`W_1 = 100 * 4 = 400 J`

`W_2 = 200 * 1 = 200 J`

`W_1 = 200 * 1 = 200 J`

`W_1 = 100 * 3 = 300 J`

So maximum work is done on

A) Using a lever to lift 100 newtons up to 4 meters on to a shelf

3)

As we know that power is rate of work done

so we have

`P = (W)/(t)`

`P = (420)/(3)`

`P = 140 W`

4)

As per energy conservation we know that

D) In a closed system, a system that isolated from its surrounds, the total energy of the system is conserved