Two men, Joel and Jerry, push against a wall. Jerry stops after 10 min, while Joel is able 1) to push for 5.0 min longer. Compare the work they do. A) Both men do positive work, but Joel does 25% more work than Jerry. B) Both men do positive work, but Joel does 75% more work than Jerry. C) Both men do positive work, but Jerry does 50% more work than Joel. D) Both men do positive work, but Joel does 50% more work than Jerry E) Neither of them does any work.

the correct answer is E

Explanation:

Work is defined by the expression

        W = F. d

Where the bold indicates vectors, we can make the dot product explicit

         W = F d cos θ

We can see that this definition of work the two men apply a force, but the wall does not move, so if there is no displacement the work is zero.

When checking the correct answer is E

A) 26.5 m/s

B) 33.0 m/s

Explanation:

A)

Once the car leaves the cliff, as no other influence than gravity acts on it, and since it causes the car an acceleration in the vertical direction only, in the horizontal direction, it keeps moving at the same speed until it reaches to the other side.So, we can apply the definition of average velocity to find this speed as follows:

       

We know the value of Δx, which is just the wide of the river (53.0m), but we need to find also the value of Δt.This time is given by the vertical movement, whic.h is independent from the horizontal one, because both movements are perpendicular each other.Since the only influence in the vertical direction is due to gravity, the car is accelerated by gravity, with constant acceleration downward equal to g = -9.8m/s² (taking the upward direction as positive).Since the acceleration is constant, we can use the following kinematic equation, as follows:

       

if we take the river level as our x-axis, this means that yf = 1.3 m and

       y₀ = 20.8 m.

At the same time, due to in the vertical direction the car has no initial velocity, this means that  v₀ = 0.Replacing by the values in (2) , and solving for t:

       

If we choose t₀ =0 ⇒ Δt = t = 2 sReplacing Δx and Δt in (1):

       

B)

When the car is just landing in the other side, the velocity of the car has two components, the horizontal one that we just found in A) and a vertical one.Due to the initial velocity in the vertical direction was just zero, we can find the final velocity just applying the definition of acceleration, with a =g, as follows:

     

Since both components are perpendicular each other, we can find the magnitude of the velocity vector (the speed) using the Pythagorean Theorem, as follows: