# Homework Help: Calculate instantaneous speed

1. Mar 2, 2013

### Zashmar

Gday mates,

This is my question
I uploaded a picture of the graph.

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2. Mar 2, 2013

### SteamKing

Staff Emeritus
The instantaneous speed is the slope of the distance-time curve at t = 30 min

3. Mar 2, 2013

### Zashmar

That is what I thought... In that case the answer would be 75k/h

4. Mar 2, 2013

### haruspex

No, it's 45kph. Pls explain exactly how you are calculating the slope.

5. Mar 3, 2013

### Zashmar

By finding the gradient of the line the 30 mins corresponds to, it is rise 3 run 4. So gradient is equal to 3/4 or 75klm

6. Mar 3, 2013

### haruspex

What are the units of each step on the y axis; likewise on the x axis?

7. Mar 3, 2013

### Zashmar

Y axes is kilometers x axis is hours

8. Mar 3, 2013

### lep11

No, x axis is minutes.

9. Mar 3, 2013

### Zashmar

Yea whoops

10. Mar 3, 2013

### haruspex

If the grid lines were km and hours then your 3/4 should have produced 0.75 km/h.
In fact, they're 5km and 5min.