How to do Uniform Motion

Question

Joe and Mary left a campsite on a trip down the river in a canoe. Joe was traveling 2 miles/hr faster than Mary. If it took Joe 4 hours to travel 20 miles, how long will it take Mary?

How do I solve this? I am very confused.

Answer 1

distance=rate*time

d=r*t

Joe: 20=r*4

r=20/4

r=5 mph

Mary's rate is 5-2=3 mph

Mary: d=r*t

20=3*t

20/3=t

t=6 2/3 hours for Mary to travel down the river

Answer 2

Hi Will,

This question is based on uniform velocity which is equal to the change in position divided by the change in time. In equation form:

v = Δx/Δt.

In your case, I'm going to use v_J for Joe's velocity, and v_M for Mary's velocity. We are told that Joe is going 2 miles/hr faster than Mary. This means that:

v_J = v_M + 2

We are also told that Joe traveled 20 miles in 4 hours. This is his velocity!

v_J = 20 miles/4 hrs = 5 miles/hr

If we know v_J we can use plug this into our equation above to solve Mary's velocity.

v_J = v_M + 2

5 = v_M + 2

v_m = 3 miles/hr

I hope that helps! If you are still confused let me know.

Bryce

Answer 3

m+2=j

(m+2)4=20

4m+8=20

4m=12

m=3

speed*time=distance