Turn on thread page Beta
 You are Here: Home >< Physics

# Help with a projectile motion problem watch

1. Someone stands on a podium 4.9m high, and throws a cricket ball for 20m. What is the speed of their pitch?

Please help. I have a few ideas about how I could get the answer but I don't know for sure. +reps galore if you help, thanks in advance.
2. (Original post by Guest5881)
Someone stands on a podium 4.9m high, and throws a cricket ball for 20m. What is the speed of their pitch?

Please help. I have a few ideas about how I could get the answer but I don't know for sure. +reps galore if you help, thanks in advance.
Which SUVAT equations have you chosen?

Hint: resolve into horizontal and vertical components by first calculating the time it takes the ball to fall 4.9m under gravitational acceleration. Then use that time to calculate how fast the ball must travel to cover the 20m horizontal distance.
3. (Original post by Guest5881)
Someone stands on a podium 4.9m high, and throws a cricket ball for 20m. What is the speed of their pitch?

Please help. I have a few ideas about how I could get the answer but I don't know for sure. +reps galore if you help, thanks in advance.
Hope I get this right :P

FIRST you have to calculate how long the ball will stay in the air, which is independent of its horizontal velocity.

1) Write down the information you have:
- S = 4.9 m (Given height in question)
- U =0 ms-1 (Starting from rest)
- V =X (We are not given nor do we need this)
- A = 9.81 ms-2 (Vertical motion so use g)
- T = ? (You need this)

2) Look at the information you have and select a SUVAT equation. In this case we don't have V, so use:
- S = UT + 0.5AT^2

3) Rearrange this to get the term, t, that you are looking for. So this becomes:
- Square root of 2S/A

4) Substitute the values into the equation and solve using a calculator to get the time for the ball to reach the ground, 0.999 seconds.

SECONDLY using the time it will be in the air and information given in the question you can simply use distance/time to calculate the speed it was thrown at assuming negligible drag.

1) Knowing the time t, substitute in the values to get the answer, 20 ms-1

All of this assumes no drag, that the height is correct etc.

Reply
Submit reply
Turn on thread page Beta

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 8, 2016
The home of Results and Clearing

### 3,715

people online now

### 1,567,000

students helped last year
Today on TSR

### A-level grade boundaries

Hang on, have Edexcel's come out already?

### University open days

1. SAE Institute
Animation, Audio, Film, Games, Music, Business, Web Further education
Thu, 16 Aug '18
2. Bournemouth University
Clearing Open Day Undergraduate
Fri, 17 Aug '18
3. University of Bolton
Undergraduate Open Day Undergraduate
Fri, 17 Aug '18
Poll

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.