# Motion of a jumper - Find the mass

#### Jess048

A high jumper falling at 3.9 m/s, lands on a foam pit and comes to rest, compressing the pit a distance of 0.43 m. If the pit is able to excert an average force of -1100 N on the high jumper in breaking the fall, what is the jumper's mass?

I don't know where to begin so anything can help!! #### Doc Al

Mentor
Hint: What was the average acceleration of the jumper during his interaction with the foam?

#### HallsofIvy

Remember that with acceleration -a and initial speed v0, the speed at time t is v(t)= -at+ v0 and the distance moved is x(t)= -(a/2)t2+ v0t. To come to a halt, v(t)= 0= -at+ v0 so requires t= v0/a second. In that time, according to the problem, the jumper moved -(a/2)t2+ v0= 0.43 m. Plug the value of t (as a function of a- you are given v0) into that and solve for a. The solve ma= F(which is given) for m.

#### Doc Al

Mentor
In applying F = ma, be sure to use the net force on the jumper. (Don't neglect his weight.)

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving